ENHANCED WOOD FUEL HANDLING:

MARKET AND DESIGN STUDIES

ETSU B/U1/00549/14/REP

Contractors

LRZ Ltd Nordistribution Ltd

Prepared by R Landen (LRZ Ltd) R Rippengal (LRZ Ltd) A N Redman (Nordistribution Ltd)

The work described in this report was carried out under contract as part of the New and Renewable Energy Programme, managed by the Energy Technology Support Unit (ETSU) on behalf of the Department of Trade and Industry. The views and judgements expressed in this report are those of the contractor and do not necessarily reflect those of ETSU or the Department of Trade and Industry.

First published 1997 © Crown copyright 1997 Summary

This report examines the potential for the manufacture and sale of novel wood fuel handling systems as a means of addressing users’ concerns regarding current capital costs and potential high labour costs of non-automated systems.

The report considers fuel handling technology that is basically appropriate for wood-fired heating systems of between c. 100kW and c.1MW maximum continuous rating.

This report details work done by the project collaborators in order to:

1. assess the current status of wood fuel handling technology

2. evaluate the market appetite for improved wood fuel handling technology

3. derive capital costs which are acceptable to customers (In practice this proved near impossible to achieve)

4. review design options

5. select one or more design options worthy of further development

The current status of wood fuel handling technology is determined, and some basic modelling to give guidance on acceptable capital costs of 100-1000kW wood fuel handling systems is undertaken. Four designs of wood fuel handling system, including three novel systems, are then identified and costed:

1. Standard Push-Rod System (Benchmark)...... £10,500 plus civil works...... £10,500(approx) Total...... £21,000

2. Ro-Ro Bin System including bin...... £12,382 Total...... £12,382

3. Top Scraper Discharge System ...... £8,194 plus container (if required) ...... £1,500 Total...... £9,694

4. Packaged Push Rod System ...... £10,275 Total...... £10,275

The three new options (2,3 and 4 above) are approximately 50% of the cost of the existing benchmark option. Thus on a 250kW installation, where the boiler alone costs c.£35k, the potential saving is about20% of overall capital costs.

A detailed appraisal suggests that the Top Scraper and the Bin System are the two most promising options, and that these should both be pursued further. Specific recommendations for further development are made. Table of Contents

1. INTRODUCTION...... 1 1.1 Capital costs of boilers ...... 1

1.2 Key issues...... 2

1.3 Wood fuel handling systems ...... 2 1.3.1 Mechanical properties of wood-chips...... 2 1.3.2 System components...... 3 1.3.3 Standard systems...... 3 1.4 Design considerations for system components ...... 4 1.4.1 Reception area...... 5 1.4.2 Conveying...... 6 1.4.3 Storage...... 7 1.4.4 Metering...... 7 1.4.5 Stoking...... 7 1.5 Handling equipment available ...... 8 1.5.1 Scraper floors...... 9 1.5.2 Walking floors...... 10 1.5.3 Cranes...... 11 1.5.4 Augers...... 11 1.5.5 Other conveyors...... 11 1.5.6 Agricultural equipment...... 12

2. MARKET POTENTIAL...... 13 2.1 Labour replacement value model ...... 13 2.1.1 Aims of the model...... 13 2.1.2 Discussion...... 13 2.1.3 Model evaluation...... 14 2.2 Conclusion...... 14

2.3 UK target markets for biomass heating ...... 15

3. DESIGN STUDIES...... 16 3.1 Design parameters ...... 16 3.1.1 Design objectives...... 16 3.1.2 Installation baseline...... 16 3.1.3 Trailer sizes and weights...... 17 3.1.4 Design challenges...... 18 3.2 Design review ...... 19 3.2.1 Standard Push Rod System (benchmark)...... 19 3.2.2 Conical Outfeeder...... 19 3.2.3 Chain Scraper...... 19 3.2.4 Push Plate System...... 20 3.2.5“Moving Floor with Holes”...... 20 3.2.6 Ro-Ro Bin System...... 20 3.2.7 Top Scraper Discharge System...... 21 3.2.8 Drive-on Packaged Push RodSystem ...... 21 3.2.9 Summary of above...... 22 3.3 Costing information...... 23 3.3.1 Common information...... 23 3.3.2 Budget costs...... 23

4. DISCUSSION...... 24 4.1 Implications of budget costings ...... 24

4.2 SWOT analysis of Top Scraper Discharge System ...... 24 4.2.1 Strengths...... 24 4.2.2 Weaknesses...... 25 4.2.3 Opportunities...... 25 4.2.4 Threats...... 25

5. SUMMARY AND RECOMMENDATIONS...... 26

6. SOURCES AND REFERENCES...... 27

7. APPENDICES:...... 28 7.1 The Ro-Ro Bin System at EcoTech ...... 28 7.1.1 Concept...... 28 7.1.2 Proposed Layout at EcoTech...... 29 7.2 Drawings of outfeeder systems (NOT AVAILABLE ELECTRONICALLY)....31 1. Introduction

The reception, storage and handling (generally referred to herein as handling) of wood fuel has proven to be an obstacle to the adoption of biomass heating in the Uk. Wood fuel handling systems can contribute a considerable proportion of the capital cost of a project, typically 50% of the cost of the actual wood boiler, and sometimes more.

1.1 Capital costs of boilers

Realistic capital costs for wood fired plant are notoriously difficult to generalise on, due to the innumerable specification differences and the low number of units sold. The following equation is based on real data, and gives a first approximation of the cost of boilers of up to 500kW capacity, complete with the manufacturer’s minimum fuel handling specification (usually a small (1-5m3) bin requiring filling by loader):

Boiler cost (£/kW) = 178.75 - (0.1575 x (Boiler MCR in kW))

The above equation yields the following table:

Boiler MCR, kW Boiler cost, £

100 16300

200 29450

300 39450

400 46300

500 50000

Some manufacturers will be more competitive at given sizes than others, depending on how that particular size fits into their standard range. Less sophisticated equipment tends to be very competitive at smaller sizes, where other manufacturers can be very expensive. The above prices include an allowance for commissioning by the manufacturer, but exclude the flue, boilerhouse, and the plumbing and electrical works of installation, which are site-specific and vary greatly.

Later in this report, a figure of c.£10.5k is derived for the typical ‘Push-Rod’ or ‘Scraper- floor’ wood fuel handling system, currently the most widely used type and taken as a standard for the purposes of comparison. This cost covers the metal parts, which then require erection within a concrete bunker, a process which has been found typically to double the cost of the metal parts. Thus £21 k would be a typical figure for a current complete wood fuel handling system for a 100-1000kW boiler. Comparison of this cost with the above boiler costs shows that the current fuel handling cost exceeds the boiler cost until the size is in excess of 100kW. 1.2 Key issues

Key factors which concern potential users are:

□ High capital costs

□ The risk of higher than anticipated labour/management costs

Labour usage in wood fuel handling can be considerable, and is often a major cost centre. Cost-effective mechanisation is therefore essential to reduce this. However, any wood fuel handling system must be able to accept deliveries from the likely vehicle types. In practice, this often entails sinking the fuel bunker below ground, with concomitant high civils costs. Additionally, large fuel handling systems often employ technology developed for district heating plant, a use far more extensive and demanding than that likely for biomass heating in the UK. It is believed that significant scope exists for reduction in capital costs by re-engineering to suit the actual requirements of users, and by reducing the civil/mechanical interface by adopting a package approach.

This report details work done by the project collaborators in order to:

1. assess the current status of wood fuel handling technology

2. evaluate the market appetite for improved wood fuel handling technology

3. derive acceptable capital costs

4. review design options

5. select an option(s) worthy of further development.

1.3 Wood fuel handling systems

This section establishes the current status of wood fuel handling technology. This is intended to serve as a reference point, and to explain concepts and terms used later in the report.

1.3.1 Mechanical properties of wood-chips

The fuel handling system is fundamental to the success of wood heating plant, and can contribute a surprisingly high proportion of the capital costs. In an oil-fired installation, oil is delivered in bulk, stored in a tank, then pumped to the burner. This is impossible with wood-chips.

Wood-chips do not flow, and cannot be pumped. This has a fundamental effect on the handling system: converging sections in hoppers are not possible, and any hopper or silo must have a fully live base to ensure discharge. When moving horizontally, chips must be propelled constantly by conveyor or auger.

When discharging wood-chips from a tipping trailer etc., it is very difficult to discharge part of a load unless the body is sub-divided. The load will often leave the body as one mass. The implication of this is that either reception areas must cope with whole loads at one time, or some form of progressive discharge (e.g. walking floor) must be fitted to the delivery vehicle.

1.3.2 System components

A wood fuel handling system may be broken down into various stages, each with specific performance requirements. These stages may be discrete or may be combined with each other in various ways, depending on the application:

1. Reception area: This must be able to receive deliveries from the required vehicle type. To minimise vehicle waiting, it may need to receive whole load(s) at one time.

2. Conveying: Wood-chips must be conveyed either to storage or, if store and reception are integrated within reception, to clear the way for further deliveries.

3. Storage: Wood-chips may be contained in a silo, or as a pile in a bunker or barn. Size of storage depends on delivery and operating schedules for plant: how long can plant operate without delivery? Outfeeding is required to remove material from store into 4. This could be conveyor/auger, or by loading shovel.

4. Metering: Regulation of store discharge rate to suit combustion. Usually controlled by water thermostat or steam pressure, but may also use flue gas temperature or lambda sensor.

5. Stoking: Delivery of fuel into combustion zone in the correct manner. May be integral with 4.

The design considerations for each system component are discussed in Section 1.4, and equipment currently available for each component is discussed in Section 1.5.

1.3.3 Standard systems

At its very simplest, fuel handling might consist of a storage barn where trailers tip the fuel, and a loading shovel which pushes up heaps in the barn and which is used to deliver bucket loads of fuel into the metering hopper on the boiler. On a small plant this may be acceptable, where a loader is available and where the manufacturer’s basic fuel hopper gives a sensible run time between refills.

Clearly, the process of discharging wood-chips from a tipping trailer or truck onto a floor or into a bunker represents no difficulty. However if the tipping area is not the boiler feed hopper, then some form of transfer is needed. In the simple case above, where a loader is available, this is feasible (although it may not be desirable). Where no loader is available, then the materials handling generally needs to be done manually, as the cost of automated handling systems is often prohibitive. Manual handling is acceptable only where cheap labour is available and where fuel burn rate is low. LRZ experience suggests that a fit operative will take c.3 hours to move 1 tonne of fuel from a stockpile about 5 metres up steps into a hopper, on a regular basis. The key issue for non-manual handling systems is the transfer of the wood-chips from the reception area into a fully automatic store. To avoid a complex and expensive system the solution to this is normally to combine the reception and storage area:

Cross auger

el ivery

Merinq/Stokinq Auger

Standard Wood-Chip Handling System

The ‘push-rod’ system represented in the above schematic features a wood-chip store sunk into an underground bunker, capable of accepting deliveries direct from a vehicle, and equipped with a push-rod scraper outfeeder. This outfeeder discharges across the width of the store, and this discharge thus requires concentrating by a cross auger to one point, where it is dropped into the boiler feed auger. This is currently the most widely used type of system. ‘Walking floor’ systems, (see Section 1.5.2) are currently a more expensive alternative to the standard type.

The walking floor and push-rod systems would typically provide several days storage, discharging directly into the boiler metering/stoking system. Such an installation is used at West Dean College, in Sussex (see ETSU report B1178). This arrangement provides a fully live storage area which can fully discharge without manual intervention. The details of their capability are discussed further in Section 1.5.

Joinery works often use circular silos connected to the dust extraction system for storage. Systems employing circular-type silos with outfeeders require that the maximum dimension of chips should not exceed 15mm generally, with an absolute limit of 25mm, and are more suitable for dry joinery waste. Push rods (scrapers) and walking floors can tolerate larger material, up to 50mm, and 75mm as an absolute maximum. The longer material can cause jamming of subsequent conveyors, but vibrating conveyors are more tolerant than rubber belts, which in turn are more tolerant than augers.

This report investigates cheaper alternatives to the systems discussed above. As it is the most widely used, the push-rod system, which would typically cost c.£21,000, is the benchmark against which alternative systems are compared.

1.4 Design considerations for system components

This section explores in greater detail the issues surrounding the design of the system components listed in Section 1.3.2. 1.4.1 Reception area

The on-site fuel stream commences at the reception area. Larger plants, with frequent deliveries, are likely to weigh all loads arriving, and probably take samples for moisture content analysis (see ETSU report B/W3/00161/REP) Smaller plants, where weighbridge utilisation will be poorer, may find it more expedient to accept deliveries on a volume basis. Automated weighbridge installations operated by the vehicle driver are available, reducing plant manning requirements. The decision on the choice of system will be made with regard to economic factors and to commercial factors, such as the nature of contract terms between supplier and purchaser.

The main cost associated with haulage is time. In order to minimise haulage costs, it is therefore desirable to avoid keeping vehicles waiting. Thus the reception area must be designed to cope with the peak flow of vehicles. In some cases, the timing of lorry movements will be restricted as a condition of the granting of planning consent. Thus a whole day's worth of deliveries may be made in eight hours or less. Also, weekends and bank holidays will cause delivery peaks both before and after. This issue is particularly important for large plants.

The site road layout must be designed to cope with the required vehicle types, and it must be easy to manoeuvre into the discharge point. Most delivery vehicles will be rear- discharge. However if curtain-siders are used, side delivery may be required. In Sweden, specialist side tipping trailers are used.

The exact nature of the reception area will depend on the installation and vehicle size. However, even a small heating plant may have to accept 20-25m23 of material at a time, such as that delivered in a large silage trailer load. Forcing the fuel deliverer to use smaller vehicles will increase the delivery cost. If the plant cannot have an adequately-sized reception area then buffer storage must be provided on-site in the form, for example, of a Dutch barn, with material being handled manually or by loader into the plant feed; additional running costs for loaders and manpower result.

There is an important conclusion from the above paragraph: even the smallest fully automated wood-chip handling system may have to accept 20-25m3 of chips at a time. Experience suggests that such a system with two scrapers will cost about £1 5k complete with civils. A larger system, as considered later in this report, will cost £21k, representing a reduction in cost per unit volume. In practice, it is rare to find such fully automated systems with boiler sizes of below 100-150kW. The implication of this is that systems of below this size will require manual or loader materials handling, and thus have restricted market potential. If the fully automated option became cheaper, in line with the objectives of this report, then such systems would be adopted at smaller plant sizes, in turn increasing the market potential at this boiler size.

As a trailer tips, the material sliding out will block its own passage unless the operator pulls forward, or unless the material is cleared rapidly. To permit this:

1. the reception area must be well below vehicle level in order to permit full discharge whilst stationary, i.e. hopper recessed into ground or vehicle on ramp, or;

2. tipped material must be conveyed away from rear of vehicle, as in a potato conveyor at the start of a grading line, or; 3. the vehicle must be able to drive into the reception area, pulling forward as it tips.

In the first case, attention must be given to preventing the vehicle from accidentally entering the hopper. This does occur from time to time with grain installations. Drive- over grids, through which fuel can be tipped, are likely to block with wood-chips, but may be used for a small distance around the hopper, to allow staff to tidy up manually by brushing the fuel through the grid. As indicated above, the low reception level option (accompanied by a push-rod system) is used as the benchmark system later in this report.

An extreme example of the second case is sometimes found in Scandinavia, where trucks unload special roll on/off (ro-ro) (q.v.) containers, in which discharge mechanisms are housed. The truck then collects an empty container and departs, minimising downtime. This option is evaluated later in the report.

The third case requires a drive-over floor such as a scraper or walking floor, or a flat- floor area for tipping equipped with novel outfeeder. These options are examined in some detail later in this report.

1.4.2 Conveying

Coneying is usually mechanical, although pneumatic systems are also used in some contexts, particularly when combined with wood-shaving/dust extraction systems. Mechanical conveyors may be of various types, which may also appear as part of the metering/stoking system. Examples are:

1. Augers

2. Chain and flight conveyors

3. Rubber-belt conveyors

4. Vibrating conveyors.

Augers are by far the most common option for heating plants of up to approximately 1 MWth, although rubber-belt conveyors are particularly suitable for very long distances and can cope with outsize material (often up to half of the belt width). Vibrating conveyors can be used for exceptionally irregular material, even for whole tree-trunks.

Conveying can be between reception and storage, and between storage and metering. For instance, an installation to burn joinery shavings may include a reception area, from where the shavings are pneumatically transported to a large silo, and out-fed as necessary. The out-fed material is then transported pneumatically to the boilerhouse, where it is fed by auger into the boiler.

Due to the restricted delivery period alluded to above, conveyors unloading in the reception area will need to cope with handling fuel at a greater rate than average boiler demand, unless buffer capacity is provided with the reception area (as is indeed usually the case). 1.4.3 Storage

As discussed above, deliveries are unlikely to be made on every day that the plant operates. Large facilities may require four days storage to cover periods such as Christmas, and to allow for bad weather impeding deliveries. At smaller facilities, storage capacity is likely to be influenced by the desired level of attendance. Domestic installations that require daily refilling by the owner are likely to prove unattractive to some potential users, yet providing larger capacity in automated rather than passive storage can be expensive. Thus a compromise has to be reached between capital and running costs. For a domestic installation, running costs can be difficult to determine.

1.4.4 Metering

Metering involves the controlled flow of the wood fuel to match some desired variable. Control strategies on wood combustion plant vary. However the common method of control for hot-water boilers is by thermostat. The thermostat can start the fuel feeder and induced draught fan, and then stop the fuel feed when the desired temperature is reached whilst leaving the draught fan to run-on for a short while until the volatiles have finished burning. The hot char is then left on the bed to kindle the next charge. Balance is achieved between air and fuel by adjusting fuel feed rate (by, for example, auger speed) and by altering fan draught (by bypass or fan speed). Often the latter function is automatically controlled between pre-set limits. Lambda sensors or flue gas thermostats are used to control combustion conditions on larger plant.

In a small plant, the metering system may start simultaneously with the conveying system. In a larger plant, the conveying system may be started by a low level sensor in an intermediate surge bin.

1.4.5 Stoking

Stoking involves the controlled introduction of fuel into the combustion chamber. It is often, but not always, integrated with the metering system. For instance, an underfeed stoker has an auger to introduce fuel under the bed, the speed of which may be controlled to adjust the feed rate. Similarly, the Twin Heat Boiler at Drayton House has a stoker auger that runs continuously but is fed by a controlled metering auger which adjusts its speed to boiler demand.

Some form of fire-check system is normally incorporated into the stoking system. This prevents fire from burning back up the stoking system, damaging components and possibly causing a larger fire. Maintaining the combustion chamber below atmospheric pressure (by use of an induced draught system) helps in this respect. However, many units designed to burn dry wood incorporate some kind of air-valve to prevent burn back. Wet wood-burning systems are less vulnerable, but still often have such provision. Drive Motor Fuel Feed Water

Metering Auger

Temperature Sensitive v

Air Valve Grate

l/V\/\/\/\/\/\/\/^\/V^

Stoker Auger

Typical Underfeed Stoking System

A dousing system will often be incorporated to extinguish any burn back that does occur. The operation of these should be regarded as a last resort, as manual intervention is often subsequently required to clear saturated wood-chips, prior to re ­ lighting the fire.

Small boilers designed to burn large pieces of dry wood, e.g. joinery waste, are often equipped with a conveyor feed system, discharging through a lock-hopper onto a grate in a fully water-cooled combustion chamber. Similarly-sized units for burning chips, sawdust etc. are often underfeed stoked by an auger.

1.5 Handling equipment available

This section is intended to be a guide to, rather than an exhaustive list of, the types of handling equipment available. Some guidance to the applicability of various types of handling equipment to the different stages of the process can be determined from the table below:

Scraper Walking Cranes Augers Conveyors

Outfeeding from Reception x x x

Conveying x x x Outfeeding from Storage x x x x xfl

Metering x x Stoking x xfl

X = suitable fl: chain conveyors Application of Handling Equipment 1.5.1 Scraper floors

The scraper floor is a simple and robust design that has found widespread use for handling inhomogeneous materials both within and outside the bio-energy industry. The design is modular, and can be constructed in various lengths and widths to cover applications from domestic heating to power stations.

The basic unit is a hydraulically-driven reciprocating spine (the push-rod), to which are attached wedge shaped lateral members. Static wedges (not shown below) are usually incorporated, these being attached to the floor. They prevent the mass of fuel from being moved back to the starting point by the scraper on its return stroke.

Motion Plan

Ram

Spine

Cross Augel Laterals

End Wall Side View

Discharge

Floor

Diagram of Scraper Floor

Several units can be assembled side-by-side, and the spine can be made in varying lengths.

Scraper floors are used in the base of reception areas, stores, and receiving bins. It is possible to drive vehicles over scraper floors, for example when tipping. However the scrapers must be designed to accept vehicle weight; this necessitates internal gusseting of the flights and, more problematically, arranging for the flights to pass the vehicle weight to the floor. The 12t axle load of a heavy goods vehicle represents a fairly significant design challenge in this regard.

The forces required to move the scraper are substantial, as the whole of the fuel depth is born by it. A heavy concrete floor is required to anchor the whole assembly, and a hydraulic power pack with sequenced valves is required; this represents a fairly substantial cost for a small installation.

A single scraper outfeed system would produce a pulsed discharge on each forward movement of the push-rod. This is not ideal for boiler feed, and can be avoided by either using two or more scrapers (an additional cost) or using a small downstream surge bin. Commercial systems normally have two or more scrapers. However single scraper systems with small surge bins directly feeding the boiler stoking auger have been seen in Finland. The use of an additional scraper requires additional fabrication and an additional ram and valve slice per scraper. However the cost of the hydraulic power pack (about £3,200) remains constant.

1.5.2 Walking floors

A walking floor consists of narrow planks, moved by hydraulic rams. These reciprocate in a pre-determined sequence, to discharge material from a silo:

Discharge

Phase 1: W hole floorm oves, carrying fuelw ih ±.

Discharge

Phase 2: One third of fbor returns to start, leaving fuel

Discharge

Phase 3: Second thiol of floor returns to start, leaving fuel in

Discharge

Phase 4: Final third of floor returns to start, leaving fuelin Process now restarts from Phase 1. Diagram of Walking Floor Operation

The width can be altered by varying the number of planks. Walking floors have particular advantages in that they can cope with outsize material, and can be driven on whilst operating, but they are expensive. Usage of this system in the UK for wood fuel handling is rare. 1.5.3 Cranes

Gantry cranes have been widely used in larger district heating and power plants. Similar in layout to a factory gantry crane, they are equipped with a clamshell grab which can be positioned in 3-dimensions, either by an operator, or more commonly by computer control.

The duty of feeding a boiler is far more severe than factory usage, and the crane needs to be more robust than its working load might at first suggest. Factory units have proven to have short lives when not correctly specified for this type of duty.

It is generally accepted that cranes are a viable option only where plant size exceeds 1.5MWth, so they are not considered further herein.

1.5.4 Augers

Augers are very popular for the dosing or metering function, as they give a very constant discharge rate, and a degree of air sealing which other conveyors do not. They do, however, require the restriction of maximum particle size, to prevent jamming. The underfeed stoker in particular requires the use of an auger, as do many small side-fed stoker systems. For this reason, underfeed type stokers require fine chips (often <20 x 12 x 3 mm), and are perhaps more suitable for the joinery industry than for SRC/Forest Waste. If fuel quality is suspect then augers are probably best avoided, though with the smallest units there is really very little option, and most small equipment uses auger feed. The use of a square stoking tube containing the auger does seem to improve fuel tolerance, by providing clearance in the corners for large pieces. Similarly, some manufacturers have arranged the auger to shear outsize pieces against a ledger plate. Such a system will cope with occasional outsize pieces, but not a persistent overload.

Specialist augers are used for the discharge, or outfeeding from bins or silos. A fully exposed auger is mounted horizontally, and allowed either to swing from side to side, or to rotate in the horizontal plane about one end. Situated at the bottom of a store, this will pull material from the whole swept arc towards the pivot point of the rotating auger, where it is discharged. Another type, the conical outfeeder uses an inclined auger to extract fuel from the converging coned bottom of a silo. The auger not only rotates, but also rolls around the cone to gather the fuel. This design is popular for joinery waste.

1.5.5 Other conveyors

Rubber-belt and chain conveyors are discussed separately from augers, the distinction being made on their material handling capabilities.

These types of conveyors are well suited to moving wood fuel over long distances, and are relatively tolerant of large pieces. Rubber-belt conveyors are similar to those used in the minerals industry, and operate in a v-section to retain the material. Provided that pieces of wood do not overhang the sides of the belt, material of up to 500mm will not cause problems. Some manufacturers specify half of the belt width as a maximum size. Maximum angle of operation is limited by fuel tumbling back down the conveyor, an effect that can be reduced by using a ribbed belt.

Chain conveyors normally consist of a pair of chains between which are stretched lateral bars, in the nature of a ladder. Such units can be assembled in various widths, and can operate at relatively steep angles. They are probably less tolerant of large pieces than rubber conveyors.

A narrow chain conveyor can be mounted on a swinging or rotating arm that moves horizontally to outfeed from the base of a store, in a similar manner to the outfeeding auger discussed above. Alternatively, the whole base of a store can be covered with a broad chain conveyor. This system has been used for buffer stores in large plants. However, there is some dispute over its reliability (q.v.).

1.5.6 Agricultural equipment

Scope exists for the adaptation of agricultural conveying equipment to wood-chip handling, in particular potato elevators and slurry scrapers, both of which show scope for handling woodchips. The suitability of agricultural equipment is limited by two factors:

1) Short design life. Many agricultural machines only operate for c.200 hours per year, so a 2000 hour design life gives 10 years operation. A power plant may require 8000 hours operation per annum, and a heating plant 2000 hours per annum.

2) Lack of warranties. Large plant, supplied on turnkey contract, is likely to have performance warranties offered by the main contractor, who will pass these back to the equipment vendors. Agricultural equipment suppliers will not be accustomed to such arrangements.

It is these differences, perhaps, that account for the large disparity in cost between agricultural and industrial materials handling equipment. If there is a role for agricultural equipment, it is probably in smaller heating projects, due to the nature of the commercial arrangements and the relatively low number of operating hours per annum. However, the remainder of this report concentrates on bespoke options purpose designed for wood-chip handling. 2. Market potential

One of the aims of this work was to identify the market appetite for investment in enhanced wood fuel handling technology. To this end, it was deemed desirable to evaluate acceptable levels of capital cost at which potential users would make the decision to invest.

An attempt was made to estimate the potential market and acceptable cost for the equipment by the following method:

1. Assessing cost-benefit of replacing labour with increased mechanisation: taking a partial-budget approach and assuming the same simple payback on capital as the basic boiler installation to yield a target capital value for the wood fuel handling system.

2. Performing sensitivity analysis with respect to plant size to determine applicable range of installation sizes: examination of various sizes of installations to show the sizes of plant where the increase in mechanisation is cost-effective and using this size data in conjunction with the British Biogen market strategy report 1 to permit the potential number of sites to identified, at least in very broad terms (tens, hundreds etc.). This was to be used to give some idea of the replication potential for costed options.

The vehicle intended for the application of this method was a ‘Labour Replacement Value Model ’. In practice, it proved difficult to obtain the necessary data to produce meaningful results. The intended model is described in the following section.

2.1 Labour replacement value model

2.1.1 Aims of the model

To assess the economic viability of mechanisation by comparing the trade-off between increased mechanisation and decreased operational costs: the labour replacement value (LRV). Parameters include: fuel usage (which is affected by plant size, full load hours and fuel moisture content), labour costs, and payback period.

2.1.2 Discussion

For an economic evaluation of new-build wood fuel handling projects it is important to first set investment criteria, such as acceptable payback periods. In a company situation, four years is a realistic period for return on capital and eight years would be a sensible maximum in a non-profit making situation. For retro-fit projects it is important to improve the payback of the overall project by the introduction of a capital intensive handling system. It is again necessary to determine the payback period of the project.

The two important remaining variable parameters which affect the viability of a mechanisation project are fuel usage and cost of labour. Using an appropriate payback

1 A Strategy to Develop the UK Market for Biomass Heating Installations by Jim Birse, British Biogen. period limitation and figures for fuel usage and labour costs, it was hoped that estimates of economically viable capital costs for increased mechanisation could be made.

It was the ultimate intention that the model would produce a range of parametric constraints to the implementation of a wood fuel handling system, e.g. ‘An automated wood fuel handling system, with desired payback of w years, can only be introduced to a site with a fuel throughput higher than x tonnes/year with a labour cost (from wood fuel handling) of y £/year giving a labour replacement value (LRV) higher than £z.’

(A more complex model could be applied to a case study situation where many more parameters are known.)

2.1.3 Model evaluation

Whilst an attempt was made to assess the market appetite for costs by the above method, this proved impossible in practice. There are several reasons for this, which serve as important indicators for future projects:

1. Assessing users’ payback criteria in general terms is very difficult: users have very different payback requirements.

2. Using the basic boiler system payback criteria as the basis for evaluating acceptable costs for the handling system is misleading. Just because a user invests at say 8- year payback in a boiler does not necessarily mean they will invest at 8-year payback in an additional handling system.

3. Evaluating current and future labour costs is almost impossible:

a) All users have different labour costs: charging full cost will make almost any wood-fired heating project unviable, however many potential users have indicated that they will use marginal labour costs, which has a major effect on viability.

b) Whilst Sandars (1995) devised regression functions for labour usage, these do not separate labour into that associated with wood fuel handling (and thus avoidable by enhanced mechanisation), and that not associated with fuel handling, (being thus unavoidable). It is therefore very difficult to assess the effect of enhanced wood fuel handling on labour usage, and thus on labour costs.

From the above it may be seen that an excessive degree of uncertainty was associated with attempting to project labour costs for current and new options, and also even if that data had been available, it would have been dubious to have converted it into capital cost figures. Therefore this aspect of the work was discontinued.

2.2 Conclusion

Because of the inherent difficulties in producing meaningful results from the labour replacement value model, quantification of the increased market penetration of biomass heating for wood fuel handling systems at different capital costs cannot be readily made. It can only be claimed that if wood fuel handling systems can be developed at a lower capital cost than standard existing systems without increasing labour requirements, then the market potential for wood as a fuel will be improved. A cost of £21,000 is used as typical of the standard Push-Rod system.

Information from the British Biogen market strategy report, which would have been used to help identify the level of market penetration possible, is given below for reference.

2.3 UK target markets for biomass heating The following table is drawn from the British Biogen report A Strategy to Develop the UK Market for Biomass Heating Installations by Jim Birse. It shows the results of market survey work undertaken by Biogen to identify the potential UK market for biomass heating on a sectoral basis:______Potential Target Markets Installation No of Installed Estimated Size Premises Capacity Annual Sales (kW) (MW) (MW) Country Estates 200 2,000 400 27 Country Houses 50 90,000 4,500 300 Farms: target sectors 20 12,500 250 12 Farms: glasshouses 1,000 2,300 2,300 153 Sports/Leisure complexes 500 1,000 500 160 Hospitals/Residential care 100 5,000 500 95 Schools, other rural 100 5,000 500 80 Schools, boarding 250 1,000 250 - Higher education 500 70 35 - Pubs/Restaurants 40 22,000 880 60 Hotels 80 3,000 240 16 Prisons 500 70 35 2

Total - 149,940 10,990 905

The markets shown are those believed to be accessible for biomass, and are mainly rural and outside mains gas areas.

Thus about 11 GW of capacity is the potentially available market for biomass heating, with an estimated replacement rate of 905MW/annum. British Biogen have identified a target of 100MW of capacity converted to biomass by the year 2000, representing a market penetration below 1% of the above total, and requiring an annual replacement rate of biomass for fossil boilers of about 3% of the above sales rate. 3. Design studies

3.1 Design parameters

3.1.1 Design objectives

The project collaborators met at an early stage to determine the key objectives that needed to be covered by the work. The following unsorted design objectives were generated at that meeting and form the basis of the work contained in the remainder of this report:

1. current handling system costs should be reduced towards a commercially viable price

2. a flat base outfeed should be incorporated, allowing mounting on an existing or new flat concrete base

3. the system should have a fully active floor, to prevent hang-ups/bridging of material

4. no civil works should be required in base (only fixings)

5. the delivery vehicle suitability to range from tractor and trailer to 38 tonne HGV if possible - (if it does not then limits should be identified)

6. storage, once closed, should be weatherproof

7. on-site works should be minimised through package design

8. the system should be adaptable to the widest possible range of sites

9. the system should require a low operator attention level

10. provision for drying should be included if possible - (this is not considered in detail further due to time constraints)

3.1.2 Installation baseline

To enable comparative costings, a base-line site specification is necessary. Based on the authors’ experience, certain key site features have been assumed:

• boiler provided by others

• stoker system, where necessary, to be provided by others

• rotary valve, where necessary, to be provided by others (optional, q.v.)

• delivery vehicle dimensions specified (see below)

• size/volume of delivery specified (see below)

These points relate back to the earlier section on System Components (Section 1.3.2). The boiler is clearly not part of the wood fuel handling package. In addition, wood-chip fired boilers are normally delivered with the stoking auger, and if necessary a rotary valve.

3.1.3 Trailer sizes and weights

Leading dimensions for the size of tipping semi-trailers commonly used for wood-chip transport are tabulated below, as well as those for a large agricultural trailer of the size that might typically be used by farmer wood-chip suppliers 2. Naturally, smaller versions of both types of trailer are available and if it proves impossible to design for the given sizes, then smaller ones could be considered. However this will limit application.

Even if it proved impossible to design for the truck size identified, then being able to accommodate the agricultural trailer would be very useful, and would indeed cover a good number of sites.

Length Width of Height off Height when Height Capacity Approx. of body body, max ground tipped of body weight full of chips

Ref on drg A C D B

Unit m m m m m m3 tonnes

Truckfl 11 2.5 1.33 9.7 2.2 55 24

Agric§ 6.81 2.29 1.27 7.53 2.31 31.5 15 fl: Fruehauf WA D SA3 Tri-Axle Step Aluminium Body Tipper, largest body version §: Griffiths GHS.140 Tandem Axle Monocoque, with silage sides

D

B

CTTT C

2 e.g. by 7-Y machinery ring for Weobley school Notes:

• The minimum width for reversing into should be 1.2m wider than the trailer (i.e. 600mm clearance each side).

• When tipped, it should be assumed that chip material will flow out en-masse of the full body size of the trailer. The height of the reception area sides must prevent spillage from a level-loaded trailer. The load will flow sideways into the extra width indicated above, and may occupy a length greater or less than that of the trailer depending on the driver ’s technique.

• It should be assumed that at time of delivery the receiving area will still contain material: perhaps up to 30% of its capacity, increasing the necessary storage capacity and length in proportion.

3.1.4 Design challenges

The following issues will need careful consideration in any system designs:

• Wood-chip build up on any floor that is not fully active.

Solutions: fully active floor, manual intervention

Problem: fully active floor can be difficult to achieve (the edges are the problem)

• Structural strength of design against vehicle and wood-chip weight

Solutions: strengthened sub-structure i.e. steel frame with concrete infill to transfer loads directly onto original concrete base.

• Vehicle dimensions, especially wheelbase width

• Single scraper leads to pulse discharge

Solutions: two scrapers, or collection pit before augering (however: civils required), or surge bin in boiler feed (with level sensor to start/stop outfeed).

• Lid for weather-proofing

Solutions: canvas foldable cover (tilt) reduces cost, provides adequate protection and can be operated by delivery man.

• Back wall pressures

Solutions: profiled/curved gates to be closed after each delivery preventing pressure build up on recovery stroke of scraper, by allowing wood-chips to relieve upwards.

• Controls: control of moving parts should be effective and cost-effective. 3.2 Design review

At an initial brainstorming, a range of options was identified and subsequently reduced to a number of proposals. Some of these are well known for wood fuel handling, but some are novel. Each was then sketched and budget costings produced. This further reduced the options to three, allowing more detailed discussion and selection of preferred options for development.

Note: diagrams of the six principle outfeeder systems discussed are given in Appendix 2.

Options identified:

3.2.1 Standard Push Rod System (benchmark)

For cost comparison purposes, it was necessary to have a control case representing current technology. As discussed in the earlier review of wood fuel handling technology, the most popular current solution for the storage and delivery of 'wet' wood-chips consists of a below ground bunker with hydraulic push rod scraper outfeeder, or an above ground bunker with ramp to reverse vehicles up to allow tipping. This meets most of the technical requirements, complying with design objectives:

2,3,5,6,8, 9 (10)

The major factor against this solution is the cost associated with the equipment and, in particular, the civils and builders attendance. It is also not packaged. This option has been costed to provide a comparison with the other costed options.

3.2.2 Conical Outfeeder

This is the standard option for free flowing dry wood waste, consisting of a cylindrical silo with a conical base containing an auger outfeeder which sweeps the whole base area. Uniquely for the systems discussed herein, this system can not accept deliveries directly from a vehicle. It does illustrate the relatively low capital cost that may be experienced when the user is prepared to transfer the fuel into the fuel silo by loader or hand. This type is widely used for joinery waste, and only rarely for wet wood waste. It is, however, a common system. It complies with design objectives:

1,4,6,7

Nonetheless, the conical section can give problems with both the freezing of the fuel during the winter months and fuel-bridging. As noted above, no provision is made for discharging fuel from a tipper truck/trailer into the silo, a major limitation.

3.2.3 Chain Scraper

This consists of two parallel conveyor chains along the bunker base, between which are mounted scraper bars. The chain returns below the base. It was used in the early days of wood handling for dry wood waste. It complies with design objectives:

1,2,3,4,5,6,7 Experience has shown that all the systems installed at boiler sites were replaced due to material being drawn under and into the chain drives and sprockets, causing the chains to go out of synchronisation and resulting in jamming of the system. However, one or two operators have had success: two installations are known in the UK and Sweden at wood fuel processing plants. Arranging the scrapers to take drive-on vehicle loads would be difficult, and this has not been seen in practice.

3.2.4 Push Plate System

This consists of a flat plate or whole cross section of a bin, propelled along the bin length by rams to discharge fuel. This design is used in some slurry spreaders. It is not known to be in use for wood-chip fuel. It would comply with design objectives:

1,2,3,4,5,6,7 & 9

A high force would be required to eject a high friction fuel such as wood-chips. Additionally, the fuel would be discharged in "blobs”, as full-height vertical slices collapsed at the outlet: without a vertically-disposed chain scraper at the discharge face, these would be difficult to manage. The authors believe that the capital cost of the hydraulics would preclude the use of this system.

3.2.5 “Moving Floor with Holes”

This is a possible cheap version of the push rod system: scrapers are provided by a moving plate covering the hopper base, with a cut away section through which the fuel discharges. One particular disadvantage is that the weight of the fuel is carried by the moving assembly, and thus substantial bearing provision is required. This design is used by Reka for their smaller systems. It complies with design objectives:

1.2.3.4.5.6.7.8.6 9 (10)

This proposal is a possible solution. Its development is in the hands of Reka.

3.2.6 Ro-Ro Bin System

This is a means of delivery utilised by some wood-chip contractors. The bin size is approximately 2%m wide x 2%m high x 5m long. The proposal is to have a push rod scraper mounted within the bin and a hydraulic system with a mechanical or hydraulic (quick-coupler) interface on the site for operating. Such a system would comply with design objectives:

1,2,3,4,6,7,9

This option is not suitable for all sites. However, where a fuel contractor operates ro-ro bins anyway it has special advantages. The conventional fuel store is replaced by a packaged delivery (analogous to a propane gas bottle), with minimal spillage. A low level of on-site works are required. The fuel outfeeder does not have to take vehicle weights. This design has been selected for the EcoTech project.

Further information on the proposed EcoTech bin system may be found in the Appendices. 3.2.7 Top Scraper Discharge System This consists of a chain scraper system uniquely working downwards through the fuel pile. It is a novel solution that is not yet available but would comply with design objectives: 1,2,3 ,4 ,5,6,7,8,9 & 10 Over and above meeting all the criteria, it has unique features for presentation, service and maintenance. The scraper does not bear weight of fuel mass and therefore avoids many of the problems such as high forces. The return of chains is over the top, so they are clear of blockage. Overall, it appears to be cost-effective, and is possibly the best candidate for development. However it is not tried or tested. It needs provision for variable height fuel discharge. A sketch of the concept, omitting the scraper flights and the sub-frame for clarity, is shown below.

Unit can ris Wood chip

Support posts Discharge

Chain Scraper flights auger

Sketch side and plan views of proposed top scraper discharge system

3.2.8 Drive-on Packaged Push Rod System

This consists of a pre-fabricated container containing a standard push rod scraper system. This would be installed on site, and would accept deliveries from vehicles reversing into the container, tipping and driving out forwards. Such a system is not currently available, but it would comply with design objectives: 1.2.3.4.5.6.7.8 & 9 (10) This option meets the design objective demands, although the cost may be increased in practice to overcome the technical challenges such as vehicle weight etc. Whilst this option was one of those initially envisaged by the authors, it has now been superseded by the other preferred options. 3.2.9 Summary of above Holes

System System System System System Scraper

Outfeeder with

Bin

Rod Rod

Plate

Chain Floor

Ro-ro Push Push Discharge Conical

Push Moving Scraper

Packaged Top

1. Reduce costs towards V V V V V V commercial price 2. Flat base outfeed V V V V V V V 3. Fully active floor V V V V V V V 4. No civils (only fixings) V V V V V V V 5. Delivery vehicle access V V V V V V V (range from tractor and trailer to 38 tonne HGV) 6. Weatherproof V V V V V V V V 7. Packaged design V V V V V V V 8. Adaptable V V V V 9. Low operator attention V V V V V V level 10. Drying if possible V V V V

Score 7 4 7 7 10 8 10 10

From the above it can be seen that the most attractive options are:

• Moving Floor with Holes • Ro-Ro Bin System • Top Scraper Discharge System • Packaged Push-Rod System

Other than the Moving Floor with Holes (which Reka has been developing), these options are costed later in this report, together with the Standard Push-Rod System, for comparison. The bin system has been included because, despite its lower score, it has very strong potential where the supply contractor operates ro-ro bins. As indicated, at least one project is proceeding on this basis at the time of writing (EcoTech: see Appendices). 3.3 Costing information

3.3.1 Common information

A number of problems would be common to all proposals, particularly in respect of: a) achieving sound structural design of container and doors etc. b) achieving suitability for alternative delivery vehicles of different sizes c) designing a weatherproof roof with appropriate manoeuvrability

The following assumptions have therefore been made: a) The containers would be of similar manufacture for all proposals (the precise specification would be subject to structural calculation). b) The containers would be based on a nominal size of 7m long x 2.5 m high x 3m wide (capacity) with the exception of the ro-ro bin system, which uses the chassis and much of the body of a standard bin of 5m x 2.5m x 2.5m. Any greater length was felt to cause severe engineering difficulties for some of the options, although it means that a full 55m3 trailer could not be fully utilised in conjunction with this size container. However a standard 40m 3 grain bulker or silage trailer clearly could. c) For the initial proposals, the roof would be of plastic coated sheet steel with a sliding front section or canvas folding cover.

3.3.2 Budget costs

Budget prices have been prepared in some detail for the chosen options: (note - all these figures include manufacturer’s margins)

1. Standard Push-Rod System in Bunker (Benchmark) £10,500 plus civils £10,500 (approx) Total...... £21,000

2. Ro-Ro Bin System including bin...... £12,382

3. Top Scraper Discharge System £8,194 plus container (if required) £1,500 Total...... £9,694

4. Packaged Push Rod System ...... £10,275 ...... Total...... £10,275

The implications of these budget costs are discussed in the next section. 4. Discussion

4.1 Implications of budget costings

Other than the Ro-Ro Bin System, each of the costed alternatives to the standard system meet all ten of the design objectives. The Top Scraper Discharge System and the Packaged Push Rod system are similarly priced. Because it could more than halve the capital cost of wood fuel handling systems, the success of one of these would be very likely to increase the market penetration of biomass heating in the UK.

The Top Scraper Discharge System has a price advantage over the Packaged Push Rod System, which also entails some significant engineering problems, not least relating to the scraper and floor strength required to take vehicle weights. Thus, while both merit further assessment, it is the opinion of the authors that the Top Scraper Discharge System is the best candidate for further development.

The Ro-Ro Bin System, while not meeting all of the design objectives, has unique advantages for certain sites and fuel suppliers. It would also be applicable for small- scale CHP or electricity only sites. Therefore, and given its relatively low cost compared to the standard system, further development is also believed to be merited and could significantly increase the up-take of biomass heating in the UK. With financial support, this could conveniently be carried out at the Eco-Tech centre in Swaffham where there is already substantial interest in the system.

Note: the cost indicated above for the Ro-Ro Bin System is based on the provision of necessary at-site works and one bin. In fact, more than one bin is required for such a system to work, since the concept entails removal on an empty bin for re-filling at the time a full bin is delivered. In a stand-alone situation, where just one heating installation used this system, two bins would therefore be required. However, in a developed market with established fuel suppliers / ESCO’s, it would clearly be unneccessary to double up bins for all sites - a ratio of 1.2-1.25 bins to every site is regarded as more likely. Nevertheless, the cost given above may be somewhat misleading and should be treated with caution. However, a further important factor is that the cost of the bins would typically be born by the fuel supplier. This would significantly reduce the initial capital outlay for the end-user which is likely to further increase market penetration of wood heating (although the cost of the bins would be reflected in the price of the fuel).

4.2 SWOT analysis of Top Scraper Discharge System

The Top Scraper Discharge System, unlike the Ro-Ro Bins, is entirely new. The authors have therefore carried out a SWOT analysis of such a system, as follows:

4.2.1 Strengths

1. Low price: due to low forces on the moving parts, as it is on top of the fuel rather than under it

2. Access & service is easier, even when full and broken down

3. Reduced maintenance cost: due to above 4. Reduced civils: only a flat floor required

5. Low running costs: low power requirement due to position of scrapers

6. Low noise level: due to low forces and power, no hydraulics required

7. Clear access for lorries/trailers: can be lifted and hinged up to leave clear access

8. Deals with a range of materials and particle sizes

9. Suitable for a wide range of vehicle sizes

4.2.2 Weaknesses

1. Large assembly

2. Not proven design

3. Health & Safety must be addressed

4. No CE approval

4.2.3 Opportunities

1. Use as a retro fit

2. Could be delivered in parts and assembled on site. This would lower transport costs

3. Use of vehicle bulk delivery outfeeder: leave trailer on-site and outfeed directly from body

4.2.4 Threats

1. Freezing of fuel at exposed top face

2. Cost of development

3. Health & Safety: moving parts are exposed rather than covered in fuel 5. Summary and recommendations

In the introduction above, two key barriers to biomass heating use were identified:

□ High capital costs of current installations

□ The risk of higher-than-anticipated labour/management costs

Automated wood fuel handling systems reduce labour costs, and it is clear that decreasing the capital cost of a wood fuelled installation without increasing labour requirements by use of cost effective mechanisation deals with both of the key obstacles. Such systems have, however, traditionally added very significantly to capital costs. Against this background, the mechanisation options detailed herein would assist significantly in improving the market potential for wood as a fuel by reducing overall capital costs and therefore increasing the number of sites where wood fuel use is viable, if they were to be developed to the point that they could enter the market.

Broadly speaking, each of the three new options identified is about 50% of the cost of the existing standard option. Thus on a 250kW installation, where the boiler alone costs approximately £35k, the potential saving is about 20% of overall capital costs.

Of the three new options, the Ro-Ro Bin System has very specific potential, and will be developed for the EcoTech project should funding be available to support this development. It is described in more detail in Appendix 1.

Of the two remaining options, the Top Scraper Discharge System has been identified as the priority for initial development. The system is described, with drawings, in Section 3.2.7., and the outfeeder system is sketched alongside alternative outfeeder systems in Appendix 2. To fulfill its potential, the system requires support for research and development, particularly in the following areas:

• detailed design of support sub-frame

• variable height discharge

• the raising mechanism

• ratio of feed to extract rates

• physical size: ie outfeed area

The authors believe there to be an additional opportunity for smaller systems of this type (e.g. less than 100kW) for farmers and estates. This could enable installation in existing oil tank bunkers and cellars etc. The equipment would require demonstration and CE approval. It is therefore recommended that every opportunity for assistance in this project be explored. 6. Sources and references

British Biogen (1996): A Strategy to Develop the UK Market for Biomass Heating Installations, by Jim Birse.

Brown, D. A. G. (1994); Coppice Wood Drying in a Gasification Plant; Stamford Consulting Group; ETSU B/M3/00388/08/REP, Harwell.

Brown, D. A. G. (1994); Drying of Coppice Wood in Store; Stamford Consulting Group; ETSU B/M3/00388/21/REP, Harwell.

dk Teknik (1993a); Facts on Installation, Operation and Economy for Wood Chip Fired District Heating Plants in Denmark; Centre of Biomass Technology, Denmark.

dk Teknik (1993b); Wood Chips for Energy Production; Technology - Environment - Economy; Centre of Biomass Technology, Denmark.

FEC Consultants Ltd. (1990); Forestry Waste Firing of Industrial Boilers; ETSU E/5A/CON/1178/1484/1560, Harwell.

Landen, R. A. & Sandars D.L. (1995); Interactive Economic Analysis of Small Scale Heating Plant, User’ s Help Manual for the Suite of Models: Heat Loss Calculator v 1.1 & LRZ Heating Model v 1.1.

Landen, R. A. & Sandars D.L. (1995); Interactive Economic Analysis of Small Scale Heating Plant, Final Report; ETSU P/01/00260/00/00, Harwell.

Landen, R. A. & Sandars D.L. (1995); Park Farm Industrial Estate: Wood Fuel Space Heating, Access Report; ETSU B/M5/00488/12/00, Harwell.

Landen, R. A. & Sandars D.L. (1995); Park Farm Industrial Estate: Wood Fuel Space Heating, Monitoring Report; ETSU B/M5/00488/11/00, Harwell.

Landen, R. A. (1994);Handling and Preparation of Wood Fuel at the Utilisation Plant; ETSU B/M3/00388/28/REP, Harwell.

Nellist, M. E., Lamond, W. J., Pringle, R. T. & Burfoot, D. (1993); Storage and Drying of Comminuted Forest Residues, Volume 1: The Report; ETSU B/W1/00146

Nordist information

Ove Arup & Partners (1989); Monitoring of a Commercial Demonstration of Harvesting and Combustion of Forestry Wastes; ETSU B 1187-P1, Harwell.

Sandars D. L. (1995); Wood Fuelled Boiler Operating Costs; ETSU B/M5/00488/22/00, Harwell.

Ward, S. & Alexander, J. (1995); West Dean Wood fuelled District Heating Scheme; Edward James Foundation/FEC; ETSU B/M5/00488/05/REP, Harwell.

Wood Fuel Handling System manufacturers literature 7. Appendices:

7.1 The Ro-Ro Bin System at EcoTech

7.1.1 Concept

The EcoTech centre requires a reliable source of wood-chip fuel for its 250kW boiler. This will be supplied by MI Edwards of Brandon. Classically, wood-chip boiler systems require considerable capital expenditure on fuel storage. M I Edwards operate a fleet of roll-on roll-off (ro-ro) bins for wood-chip transport. Closely related to the units used by waste contractors and scrap metal merchants, these hold about 35m 3 of wood-chips, or roughly eight tonnes.

This containerised delivery system has good potential for adaptation to include handling equipment, permitting the delivery of packaged fuel and subsequent usage directly from the package, without spillage or costly fixed storage silos.

The sequence of operations is as follows:

1. full bin of chips arrives on trailer behind fast tractor

2. driver reverses trailer to side of boilerhouse

3. driver unloads and locates full bin

4. driver loads empty bin

5. tractor/trailer leaves site

This is a simplified version - in practice some shuffling of bins may be required on site. However, the basic design makes this readily achieved. The bins have rollers on their rear end which makes it possible to move them without fully loading onto the trailer. 7.1.2 Proposed Layout at EcoTech

7.1.2.1 Plan layout view

Bin 2

Dischargeconveyo

Bin 1

Reception hopp Boiler feed ar

Boiler House

The bins will be located to the side of the boilerhouse on the concrete pad provided. One or two bins may be on site at one time: most of the time there is likely to be one: Bin 1 above.

7.1.2.2 Rear view of layout

Bin discharge conveyors

in 1 Bin 2 Boiler Hou

Boiler feed augeReception hopper

Both bins have fold-away discharge conveyors which carry the fuel to the reception hopper (see under operation below). 7.1.2.3 Detail of bin rear

Lid

Delivery conveyor

Discharge opening

Cross

Bin discharge is to be by hydraulic scraper floor or by chain scraper. The former require the provision of a hydraulic power pack on site. This, however, removes the need for flying electrical leads. The discharge from the full width of the bin will be collected by the transverse cross conveyor, and transported to the delivery conveyor. Operation of these conveyors will be possible regardless of whether the bin discharge system is operating or not. Their drive would be electrical or hydraulic as required.

7.1.2.4 Operation

• One bin will cover normal weekends. However two might be required for bank holidays etc. if the boiler is operating at full load.

• The reception hopper is to hold sufficient fuel to permit the driver to remove empty Bin 1 and to move Bin 2 into its place, perhaps also replacing Bin 1 with a full bin. This will require perhaps 30 minutes capacity in this hopper.

• Discharge will be via an opening in the rear of the bin, delivering onto a cross conveyor. This will in turn discharge onto an inclined delivery conveyor. Bin 1 will delivery directly, using this conveyor, into the metering hopper. When present, Bin 2 will deliver onto and via Bin 1’s conveyors into the reception hopper.

• One bin will operate at a time. Automatic changeover between bins will occur after the first is empty. The discharge sequence, and whether one or two bins are to be in use, will be manually selectable.

• When Bin 2 is delivering, Bin 1’s conveyors will run, but its discharge mechanism will be stopped.

All conveyors and the reception hopper will be protected against the weather and to meet H&S requirements.

7.1.2.5 Interface

The boiler feed auger and any airlock will be provided by the boiler supplier. This shall be positioned so as to permit the attachment of the reception hopper in such a manner as to permit discharge into the auger by gravity. The reception hopper shall be supplied and erected by the bins supplier.

A 32A 400V three-pole and neutral supply protected by a class C MCB and earth leakage protection will be required in the boilerhouse. This will be used as the supply for the bins control panel, which will be provided by the bins supplier. There will be no direct electrical connection between the bins control and the boiler or system controls. The bins system will respond to a command signal provided by a level sensor in the reception hopper. A separate low-level sensor in the bin could be used for an alarm signal to the BEMS, to indicate loss of fuel supply to the operator and to allow for re-sequencing of the boilers to gas lead.

If electrically powered, the bins will be connected to the controls by a flying lead and connector, the connection being made within a locked box (to prevent tampering). If hydraulically powered, connection will be made by hoses and hydraulic quick-couplers. The control panel would probably best be located external to the boilerhouse to permit its operation by the delivery driver without needing boilerhouse access.

7.2 Drawings of outfeeder systems

See attached wallet. (NOT AVAILABLE ELECTRONICALLY)