A Clean, Efficient System for Producing Charcoal, Heat and Power (Chap)
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Fuel 85 (2006) 1566–1578 www.fuelfirst.com A clean, efficient system for producing Charcoal, Heat and Power (CHaP) C. Syred a,*, A.J. Griffiths a, N. Syred a, D. Beedie b, D. James c a Cardiff School of Engineering, Cardiff University, Queens Buildings, The Parade, Newport Road, Cardiff CF24 0YF, UK b BioEnergy Devices, Unit 28, St Theodores Way, Brynmenyn Industrial Estate, Bridgend CF32 9TZ, UK c James Engineering Turbines Ltd, 5 St Johns Road, Clevedon, Somerset BS21 7TG, UK Received 13 March 2005; received in revised form 12 October 2005; accepted 26 October 2005 Available online 5 December 2005 Abstract There is a strong domestic and industrial market for charcoal in the UK and is still used in many developing countries for cooking and heating as well as for many industrial applications. It is usually made in small-scale simple kilns that are very damaging to the environment, very inefficient and labour intensive. The Charcoal, Heat and Power (CHaP) process offers a method for producing clean efficient charcoal under pressurised conditions and uses the product gas from the carbonisation process to drive a small gas turbine to produce heat and power. The charcoal is produced using waste forestry matter and other waste wood, including that from sustainably managed forests. The CHaP system can also be used in developing countries where there is an excess of forestry waste and a shortage of fossil fuels. The CHaP process was initially designed, developed and a prototype system built. This paper discusses the CHaP design and the various components used, their separate development and integration into a system. Tests showed the process successfully produced a high quality charcoal and the product gas effectively used to drive a gas turbine. The CHaP technology was proven and a new novel system of producing charcoal under pressurised conditions was created coupled with a novel use of the product gas whose output was green heat and power. The initial CHaP prototype showed the process was capable of producing low emissions and is virtually carbon neutral. q 2005 Elsevier Ltd. All rights reserved. Keywords: Charcoal; LCV wood gas; Combustor; Small gas turbine 1. Introduction (another by-product of charcoal manufacture) was used by the Egyptians as an embalming material [1]. Long before its development as a fuel, charcoal was used as The production of charcoal involves burning the raw a drawing medium by artists. Cave paintings made with material in an atmosphere free of oxygen (or air) and the charcoal have been found, dated to 30,000 years BC. The earliest method of charcoal production was probably with a pit ‘charcoal’ used here was more likely to be charred sticks from kiln, positioned in the forest, close to the point of wood a fire, rather than charcoal produced intentionally. The bronze collection. This involved digging a shallow, level, pit and and iron ages, starting around 5500 years ago, are probably the stacking the timber to be used longitudinally along the bottom first use of charcoal as a fuel. Wood could not produce the high of the pit. The complete pile was covered with vegetation, temperatures needed to smelt, or reduce the ores, and then to straw and earth to make an airtight seal around the wood. The melt the resulting metal in order to cast it. Copper was first wood was lit and the burning allowed to progress from one end reduced with charcoal around 3000 BC, starting the Bronze of the pit to the other, a process taking around 10–15 days [2]. Age, and around 1200 BC, the Iron Age began. It is possible Further developments led to the classical ‘forest kiln’, a that the Egyptians also used charcoal in the early development hemispherical woodpile built around a central shaft, which of glass. A by-product of producing charcoal, tar or pitch, was acted as a chimney. Again, the woodpile was covered with soil used to waterproof wooden structures, in particular ships, as far and turf to shut out the air, and lit by pouring several bucket back as Roman times. In addition, the pyroligneous acid loads of hot embers down the chimney, which was then sealed. Air supply to the heap was controlled by ensuring that any * Corresponding author. Tel.: C44 29 2087 4318; fax: C44 29 2087 4317. cracks in the earth covering were repaired and opening or E-mail address: [email protected] (C. Syred). closing purpose-made vents built at the base of the woodpile. 0016-2361/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. The charcoal burner had to attend to the kiln throughout the doi:10.1016/j.fuel.2005.10.026 burn to ensure that maximum charcoal was produced without C. Syred et al. / Fuel 85 (2006) 1566–1578 1567 the wood being burned to ashes, a process which would take Charcoal in Europe is mainly used for the barbeque market, around 10 days. During this carbonisation process, the pile although there are many other uses and the UK imports over would contract in size as the volatile matter was lost from the 90% of its requirements. Interest is also growing in charcoal wood. Average yield of charcoal from this type of kiln was as a ‘renewable’ fuel. Developing countries and those short of around 35–40 bushels of charcoal per chord of original wood fossil fuels however, use charcoal as their main cooking fuel (i.e. around 35–45% of the original volume) depending on as well as for many industrial processes, such as smelting and operating conditions and wood-type. One major disadvantage steel refining. Charcoal can also be ‘activated’ by further with this method of charcoal production was that a percentage refining and in this form is used in filters for water and air. of the feedstock was burned to produce heat in order to power Charcoal can be used for medical purposes, both internally the carbonisation process [1]. and externally. It is used in sugar refining, agriculture, horticulture, and as an ingredient in animal foodstuffs. 2. Charcoal production developments Specific charcoals (i.e. those resulting from particular wood species) are used for gunpowder and fuse powders, and also Improvements to the traditional forest or pit kilns involved for artist charcoal. building more permanent structures with bricks and more The Charcoal, Heat and Power (CHaP) process discussed in recently, metal. This, however, presented the problem of this paper offers a cheap, clean and efficient method of transporting large amounts of wood from the forest where it producing charcoal with the waste energy being utilised in the was felled to the site of the carbonising facility. Initially, the production of heat and power. This process can be used in first development was to replace the forest kiln with a very many situations both nationally and internationally. In the UK similar structure built with brick bases, in order that the tar and the CHaP system could be used at forest management sites, pyroglineous acid could be collected in pits and put to further also with traditional and urban forestry. The completed system use. Later, domed brick kilns were built, which were uses wood sustainably derived either from ‘urban forestry’— themselves replaced with cast-iron retorts, where the wood to highway, amenity and domestic tree management operations— be carbonised was held in a cylinder separate to the fuel used to or from revitalised deciduous woodlands. It could, if required, provide heat for the process. In this system, a brick-built utilise wood-chips from ‘energy plantations’ or waste from chamber incorporating a firebox remained hot while the cast- conventional forestry. In developing countries, the CHaP iron cylinder holding the wood could be rapidly replaced, system could with modifications, use a range of different saving time and heat energy. Quite a number of different biofuel and biomass materials. With increasing concerns over designs were produced using this basic design principle, with climate change and the UKs commitment to increasing green additions for collecting the tar, acid and wood-gas by-products energy, reducing CO2 emissions, the process can make a useful of the process. contribution to sustainability. The process can also use a During the late 19th and the 20th century, much larger sawdust fed gasifier to provide heat to feed the carbonisation industrial plants were built for larger quantities of charcoal to process of the lumpwood. The hot gas (volatiles, tar, etc.) be produced. Here, the wood and the final charcoal products driven off from the wood, combined with the gasifier gas, is were held in railway-style wagons, which were pushed on then fed into a combustor. This combustor then fires a small gas tracks into cast-iron tunnel retorts, and pulled out at the far side turbine to produce green heat and power. The whole system is when the process was complete. In some designs, the gases operated under pressure. The CHaP system is thus an attempt to produced by the carbonising wood were burned directly in the improve the efficiency of the charcoal manufacturing process furnace, reducing the fuel requirements of the system. A large by utilising available energy to generate electricity and heat system was developed for refining and treating the by-products efficiently and economically whilst also reducing emissions. of the carbonising process, similar in form to the plant used The original system had a number of features in order to today for refining oil. A number of large charcoal producing achieve these aims: plants were built, incorporating both retorts and refinery processes, enabling both charcoal and many other products to 1. As the carbonisation of wood is a cyclic process, a be produced, thus providing the raw materials for a wide range modulated source of heat is required that can serve to of other processes [2,3].