Drying Technologies for Sewage Sludge

Drying technologies for sewage sludge

www.andritz.com Sewage sludge treatment Reuse - Reduce - Recycle System solutions from a single sorce From waste to valuable substance by drying

1.000 kg 160 kg 44 kg 20 kg

Wet sludge Dewatered sludge Dried sludge Ash 4% DS 25% DS > 90% DS 0–3% organic 40–80% organic in DS 40–80% organic in DS 40–80% organic in DS > 99% DS Agricultural utilizaton MATERIAL ENERGETIC Alternative fuel - fertilizer - coal-fired power plant - landscaping - waste incineration plant Mechanical waste water Dewatering Drying Thermal utilization treatment Belt presses, Belt-, Drum- and - direct with EcoDry Sieves, Decanter centrifuges, Fluidbed drying systems - external (industry, agri- UTILIZATION Screens, Filter presses culture) Sand filters

Energy self-sufficient mono-incineration

Nutrient utilizatoin Utilizsation in the - phosphor recycling cement industry

The road from being a waste product to thermal and one that can produce both useful material substantial utilization and energy (dry granulate) with ANDRITZ SEPARATION’s thermal process provides Co-incineration in coal-fired Cement industry, the following special features: power plants and waste fertilizer, phosphor incineration plants, cement recycling industry •• considerable reduction in the sewage sludge volume to be disposed of Significant reduction in ence, numerous references, and a world- This Class A granulate features the follow- •• alternative fuel generated with a calo- weight and volume by wide service network make ANDRITZ ing properties: rific value comparable to that of lignite SEPARATION a leading global supplier of •• substitute fuel with carbon neutral •• Thickening mechanical and thermal sludge treatment ▪▪ Dry substance content > 90% DS properties •• Dewatering systems. Sewage sludge as a final prod- ▪▪ Low dust content •• natural nutrient reserves •• Drying uct of wastewater treatment is upgraded ▪▪ Good handling properties •• Incineration to a valuable substance (dried granulate) ▪▪ Biologically stable (hygienized) by drying. A broad product range, extensive pro- As a result, both the material and the ener- cess know-how, many years of experi- gy contained in the granulate can be used in different ways.

2 3 The right thermal process for each application Three technologies to offer custom-tailored solutions Three possibilities for the optimum path from waste to product

Condensation Belt dryer (BDS) (heat recovery possible) ▪▪ for small to medium evaporation capacity Dewatered sewage sludge Exhaust air treatment ▪▪ to make use of waste heat with temperatures > 90°C evaporated Drum drying system water for and heating steam < 6 bar Preferred (DDS) cleaning heating systems

Direct with exhaust gas

350–600°C Fluidized bed dryer (FDS) Dried granulate ▪▪ for medium to large evapo- >90%DS ration capacities Coal-fired power plant ▪▪ if heating media >180°C and Belt drying system (BDS) heating steam > 6 bar are available Waste heat (steam, exhaust gas, hot water) < 90°C Cement factory

Drum dryer (DDS)

▪▪ for medium to large evapo- Fluidbed drying ration capacities system (FDS) Cyclone ▪▪ to make use of natural gas, Waste heat (steam, exhaust gas) ANDRITZ EcoDry biogas, or heating oil >150°C

▪▪ if granulate has to meet strin- Indirect with thermooil or steam

gent demands (for fertilizer) Fertilizer

With belt, drum and fluidized bed drying, ANDRITZ SEPARATION has Your advantage three technologies that offer custom-tailored solutions to the various cus- tomer requirements.

4 5 Belt drying system Ideal for making use of waste heat Recovery of material and energy content taking waste gas heat from cement production as an example

By creating a thermal and material link be- ash is used as an additive in cement pro- tween a sewage sludge drying plant and duction and thus reduces the amount of a cement kiln, an innovative concept is minerals used. obtained for conserving resources (energy and minerals). The advantages ▪▪ 100% of the sewage sludge heating Here, the thermal energy for drying the value and ash are used in cement pro- sewage sludges comes entirely from the duction waste gases from the clinker cooler in the ▪▪ Considerable reduction in operating cement works. The dry granulate is pro- costs by substituting primary energy duced from the dewatered sewage sludge, and minerals which serves as carbon neutral auxiliary ▪▪ Substitute fuel that is carbon neutral fuel in the cement kiln to generate heat for

cement production. The sewage sludge Belt drying plant, Hereke, Turkey

Pre-heater

Dried sewage sludge granulate as alternative fuel

Belt drying plant, Clos de Hilde, France Electric filter The Process perature of the drying gases (< 150°C) and ▪▪ Combination of tried-and-tested com- Exhaust air/thermooil heat exchanger The ANDRITZ SEPARATION belt drying the low dust content in the system facilitate ponents from ANDRITZ SEPARATION system granulates the dewatered sludge in safe operation. sludge drying technologies. Rotary kiln a mixer with product that has already been ▪▪ More than 30 reference plants drying dried. The moist granulate produced here is The dried material is not exposed to me- around 800,000 t of dewatered sludge distributed evenly over the belt in the dryer chanical stress during drying and is also per annum. Clinker cooler Thermo oil circuit by a specially designed feed module. The pre-cooled before the dryer discharge. even layer of material on the belt creates optimum conditions for even distribution of The technology - simple, convincing, the drying air. and successful ▪▪ The belt dryer is particularly attractive This, in turn, is necessary for even heating economically because it uses waste and drying of the sewage sludge. heat with a low temperature. ▪▪ Highly product quality of different The layer of material on the belt forms a sludges qualities due to variable back- Belt drying system BDS filter medium for the air flowing onto the feeding. granulate layer from above and thus pre- ▪▪ Modular structure and simple design vents entrainment of dust. The low tem- ▪▪ High availability. Flowsheet of a belt drying plant using waste heat

6 7 Fluidized bed drying system Drying in a closed inert gas loop Energy-optimized integration of sewage sludge drying in sewage treatment plant operations

The heat for drying the dewatered sewage Advantages for the sewage treatment sludge is taken entirely from the sludge gas. plant operator The sludge gas is used to heat the fluid- ▪▪ Significant reduction in the residual ized bed dryer with an efficiency of >90% substances leaving the sewage treat- in modern incineration plants. ment plant At the same time, the fluidized bed dryer ▪▪ No additional costs for thermal energy provides the thermal energy to heat the di- needed in drying gester. In the drying process stage the sew- ▪▪ Environmentally friendly concept to age plant produces a valuable substance conserve resources by – reducing the (dried granulate), which is in demand as transport capacities for the sewage substitute fuel in cement production or in sludge and – producing a carbon neu- coal-fired power stations due to its calorific tral substitute fuel. value comparable to that of lignite and its carbon neutral combustion properties. Fluidized bed drying plant, Bailonggang, China

Fluidized bed drying plant, Madrid, Spain Digestion tower The process The technology - simple, convincing, Sewage sludge drying at the highest Mechanical dewatering Fluidized bed dryers for drying dewatered and successful level of safety engineering sewage sludge operate in a closed inert ▪▪ Sludge feed without dry granulate – Sewage sludge with >90% dry substance gas loop. The entire heat required to evapo- backfeeding offers substantial flex- is an organic material that is combustible rate the water is fed to the dryer via heat ibility in adapting to different sludge and – under certain conditions – potentially exchangers, i.e. without any direct contact qualities. explosive. between the heat transfer medium and the ▪▪ High safety level due to drying opera- product. tion under inert gas conditions Operations under inert gas conditions as The dewatered sewage sludge is pumped ▪▪ Automatic operation (no personnel used in fluidized bed drying guarantee Hot water for digestion tower heating directly to the fluidized bed dryer without any present during the night and at week- safe plant operation in all operating modes pre-mixing, broken up using a mechanical ends) is possible and is also practiced (start-up, shutdown, stationary, upset). breaker, and then mixed into the dried granu- in many plants Thermo oil late which is held in motion by the fluidizing ▪▪ High thermal efficiency due to closed These inert gas conditions are maintained gas. Due to the excellent heat and material gas loops from the dryer, to product cooling, to stor- transfer conditions prevailing in the fluidized ▪▪ Low waste gas volume (<200 m3/h) age. Digestion gas bed, the sewage sludge fed to it is dried at due to closed design reduces expendi- 85°C to >90% dry substance in a very short ture for waste gas cleaning. time. The fluidized bed dryer uses waste ▪▪ More than 30 reference plants in op- heat from industrial processes, but also pri- eration all over the world. Fluidbed drying system mary energy. ▪▪ High plant availability and proven op- Thermooil boiler At the same time, waste heat at a tempera- erating times of >8000 h per annum ture level of 60°C is available for further use.

Flowsheet of a fluidized bed drying plant

8 9 Drum drying system Drying and granulating in a single step Energy efficiency from combined heat and power generating (with a gas motor for example)

The electric current for operating the sew- The advantages age sludge drying plant is supplied by a gas ▪▪ Having no direct contact between motor operated as a co-generation unit. CHP waste gas and the dryer system results in simple safety management The thermal energy required for drum dry- ▪▪ Fast and easy switch online from CHP ing is provided from the gas motor exhaust mode to burner mode without impair- air and also from their cooling water shell. ing product quality Efficient heat recovery is a very important ▪▪ Efficient heat recovery factor. Integration of CHP (Combined Heat and Power) reduces carbon and exhaust air emissions by up to 20% due to direct use of waste gas and greater efficiency of CHP compared to power plants.

Drum drying plant, Paris, France

Stack

Drum drying plant, Ashford, UK Condenser The process The technology - simple, convincing, pressure Gas Engine Cooling Water Cooling Water The ANDRITZ SEPARATION drum drying and successful • Evenly dried right through and hy- Heat Exchanger process is one of the oldest processes for ▪▪ Low energy consumption due to spe- gienized drying sewage sludges. Dewatered sew- cial drum design • Easy to store and dose, excellent han- Cooling water pump Circulation age sludge is mixed in a mixer to a dry con- ▪▪ Low-odor operations due to partial dling properties air fan tent of approximately 60% DS with material vacuum in the drying system • Dry granulate particularly suitable for that has already been dried. ▪▪ Small volume of exhaust air due to material use (as fertilizer) closed circulating air loop The pre-granulated moist granulate is fed ▪ Long plant service life by using sturdy Drum drying - successful for 40 years ▪ Exhaust Gas Air Cooler to the triple pass drum. The hot gas flowing plant components, short conveying ▪▪ Up to 12 t/hr water evaporation per line Heat Exchanger through the drum transports the pre-granu- routes, and compact design ▪▪ Around 70 drum drying plants installed Gas Eingine Exhaust Gas lated sewage sludge, and water contained ▪▪ ABIS – Advanced Burner Inertization worldwide for drying over 5.6 million in the sludge is evaporated at the same System – to obtain a low-oxygen gase- tons of dewatered sludge per annum, Separator time. In the slowly rotating triple pass drum, ous atmosphere in the dryer’s circulat- resulting in 4 million tons of water Furnace Head which is made up of concentric cylinders, ing air system when the plant is shut evaporation per annum and 1.2 mil- the product is shaped into round granulate down. lion tons of granulate for further use due to the constant rolling movement. The final product The final product is a largely dust-free, dry • Dry content 92–95% DS Gas Engine Generator Furnace Drying drum granulate with 92–95% DS. • Largely dust-free and stable under

Flowsheet of a drum drying plant (example with gas engine)

10 11 Safety engineering in ANDRITZ SEPARATION drying plants In this sector, dust explosions bear the highest risk potential. Measures must be implemented to prevent damage to individuals and to equipment as far as possible. Three requirements must coincide to create a dust explosion:

Spark detection

If at least one of these requirements can be reliably excluded, there will be no explosion.

The primary safety measures derived from this and which are implemented in ANDRITZ SEPARATION belt dryers are strong dilution of any dust concentrations occurring, as well as monitoring of these concentrations and shutdown if approximately 10% of the lower explosive limit is reached. Consistent operations under depleted oxygen atmosphere in all conceivable operating modes, as practiced successfully in fluidized bed and drum drying plants for more than two decades, mean that it is impossible for explosive mixtures to form. This primary explosion protection guarantees the highest level of safety engineering. Explosion extinguisher

In addition to these primary protection measures, the following secondary measures are used, depending on the drying system concerned, in order to minimize the effect of possible explosions on man and machine as far as possible.

Explosion suppression Use of constructive explosion protection measures, such as explosion suppression or explosion pressure venting, e.g. for dust separators (filters, cyclones) and silos. Safety has top priority in ANDRITZ Use of CO measurements for early detection of self-ignition processes or overheating.

SEPARATION drying plants for sewage Fire-fighting equipment (CO2, N2 or sprinklers) sludge. Dried sewage sludge is an organic Eliminating the risk potential by minimizing dust accumulation and swirling and by cooling substance that the product ▪▪ is combustible, ▪▪ has a calorific value comparable to that A careful analysis (ATEX) of the sewage sludge drying plants in consideration of the ATEX of lignite, directives (particularly 94/9/EC) and the related harmonized standards (particularly EN 1127- Sprinkler system in a belt dryer ▪▪ is susceptible to self-ignition, and 1) is essential, particularly during start-up and shutdown procedures and in the event of ▪▪ can form explosive mixtures of dust and air. malfunctions.

Control panel of a Safe-T-Box for belt drying plants

12 13 Service offered for drying plants It is part of the ANDRITZ SEPARATION strategy to provide high-quality equipment. ANDRITZ SEPARATION helps its customers to Service ANDRITZ SEPARATION offering for maintain the profitability and the value of their drying plants for many years. ANDRITZ SEPARATION offers performance assessments by specialists service contracts and upgrades in addition to service and maintenance, with the aim of optimizing the operating conditions and thus also the profitability of customers’ plants. ANDRITZ SEPARATION service specialists ▪▪ Fixed and thus calculable mainte- ▪▪ Audits for performance and safety en- help customers to keep machine and plant nance costs gineering assessments of drying op- availability as high as possible. ▪▪ Regular inspections and process operations timizations ▪▪ Consulting on optimization/rebuild of ANDRITZ SEPARATION as system provider ▪▪ Preventive maintenance drying systems and process know-how owner is aware of ▪▪ Targeted stocking of spare parts the many ways of optimizing a plant, re- ▪▪ Diagnosis services via modem or special ducing the operating costs, and increasing measuring equipment (e.g. endoscopy) performance. ▪▪ Maintenance and operating training for personnel In addition, ANDRITZ SEPARATION assists ▪▪ Modernization the operators of drying plants to keep their ▪▪ Available 24/7 plant in line with the latest technical and ▪▪ Identifying potentials to reduce operat- safety demands required by law. ing costs ▪▪ Payments tied to achievement of targets ANDRITZ SEPARATION leads the market ▪▪ Lists of spare and wear parts so that in dryer plant safety, setting benchmarks orders can be dealt with promptly for safe plant control and equipment, and ▪▪ Involvement of sub-suppliers for full is thus the ideal partner in matters relating plant service to plant safety.

14 15 System solutions for sewage sludge Worldwide successful

Fluidized bed drying Energy efficient and environmentally friendly With the sewage sludge drying plant in Shanghai Bailonggang, the largest sewage treatment plant in Asia, the three lines forming this fluidized bed drying plant are making a further contribution towards environmentally friendly disposal of the sewage sludges produced in wastewater treatment. The energy combination between digestion and drying permits high energy efficiency with the digester gases generated in the digester towers.

Belt drying Use in the cement industry - sludge disposal with no residue The order carried out for a European cement factory contains the world’s largest belt drying plant, with a water evaporation rate of 8 t/h. 100% of the thermal energy used to heat the dryer in the plant is recovered from the waste gas from the cement factory. The plant supplied incorporates one of the most modern and innovative concepts for protection and conservation of resources.

Drum drying The world’s largest drying plant for sewage sludge The water treatment plant in Changi, Singapore, was the first phase of the Deep Tunnel Sewerage System (DSTS). The drum drying plant, comprising five DDS 110 lines, is part of the solids process and is still the world’s largest plant of its kind today, with a water

evaporation rate of 11,200 kg H2O/hr per line.

We offer … ▪▪ Complete solutions for new plants ▪▪ Modernization and upgrades of existing plants ▪▪ Service and maintenance from specialists with over 40 years experience in the field of thermal sewage sludge treatment.

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