Energy Recovery from Litter: A Guide for Users

Transcription

1 Energy Recovery from Litter: A Guide for Users by S.G. Wiedemann (FSA Consulting) JULY 2015 RIRDC Publication No. 14/096

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3 Energy Recovery from Litter: A Guide for Users by S.G. Wiedemann (FSA Consulting) July 2015 RIRDC Publication No. 14/096 RIRDC Project No. PRJ

4 2015 Rural Industries Research and Development Corporation. All rights reserved. ISBN Energy Recovery from Litter: A Guide for Users Publication No. 14/096 Project No. PRJ The information contained in this publication is intended for general use to assist public knowledge and discussion and to help improve the development of sustainable regions. You must not rely on any information contained in this publication without taking specialist advice relevant to your particular circumstances. While reasonable care has been taken in preparing this publication to ensure that information is true and correct, the Commonwealth of Australia gives no assurance as to the accuracy of any information in this publication. The Commonwealth of Australia, the Rural Industries Research and Development Corporation (RIRDC), the authors or contributors expressly disclaim, to the maximum extent permitted by law, all responsibility and liability to any person, arising directly or indirectly from any act or omission, or for any consequences of any such act or omission, made in reliance on the contents of this publication, whether or not caused by any negligence on the part of the Commonwealth of Australia, RIRDC, the authors or contributors. The Commonwealth of Australia does not necessarily endorse the views in this publication. This publication is copyright. Apart from any use as permitted under the Copyright Act 1968, all other rights are reserved. However, wide dissemination is encouraged. Requests and inquiries concerning reproduction and rights should be addressed to RIRDC Communications on phone Researcher Contact Details Stephen Wiedemann FSA Consulting PO Box 2175 TOOWOOMBA QLD 4350 Phone: Fax: stephen.wiedemann@fsaconsulting.net In submitting this report, the researcher has agreed to RIRDC publishing this material in its edited form. RIRDC Contact Details Rural Industries Research and Development Corporation Level 2, 15 National Circuit BARTON ACT 2600 PO Box 4776 KINGSTON ACT 2604 Phone: Fax: rirdc@rirdc.gov.au. Web: Electronically published by RIRDC in July 2015 Print-on-demand by Union Offset Printing, Canberra at or phone

5 Foreword The Australian Chicken Meat industry has identified new opportunities for utilising spent chicken litter as a feedstock for bioenergy production. Traditionally, spent chicken litter has been applied to land as a fertiliser and soil conditioner and this is currently the largest and most important end use for poultry litter. However, opportunities may exist in the future to utilise the energy value of litter with a number of different bioenergy production techniques, producing bioenergy and valuable fertiliser products. These technologies range from mature to prototype, and very few have been applied in the Australian chicken meat industry. This guide aims to outline the characteristics of chicken litter as a feedstock, and identify the main technology options available for bioenergy production. The guide acts as an entry point for interested poultry producers, with references to more detailed research project reports. This information can be used by various sectors of the chicken meat industry to begin the process of evaluating the economic and environmental potential of converting by-products from the production of chicken meat into energy and organic fertilisers. This project was funded from industry revenue which was matched by funds provided by the Australian Government. This report is an addition to RIRDC s diverse range of over 2000 research publications and it forms part of our Chicken Meat R&D program, which aims to stimulate and promote R&D that will deliver a profitable, productive and sustainable Australian chicken meat industry. Most of RIRDC s publications are available for viewing, free downloading or purchasing online at Purchases can also be made by phoning Craig Burns Managing Director Rural Industries Research and Development Corporation 5

6 Contents Introduction 7 Energy generation technologies 8 Thermal processes 8 Anaerobic digestion 8 Composition and characteristics of chicken litter 9 Combustion 11 Feasibility of process 12 Gasification 13 Feasibility of process 14 Pyrolysis 15 Feasibility of process 15 Biochar 16 Anaerobic digestion 17 Feasibility of process 18 References 20 Table index Table 1. Moisture content of spent litter from different bedding materials. 9 Table 2. Summary of estimated content proportions in Australian chicken litter. 10 Figure index Figure 1. Products and pathways for biochemical and thermal processing of biomass. 8 Figure 2. Direct combustion flow chart. 11 Figure 3. Gasification flow chart. 13 Figure 4. Schematic diagram of a typical plant set-up. 15 Figure 5. Combined leach bed & high-rate anaerobic system for poultry litter. 17 Figure 6. Payback period dependent on digestibility. 18 Figure 7. Anaerobic digestion technologies compared. 18 6

7 Introduction Chicken litter from chicken meat production is a high volume by-product which has properties that may be suitable for energy production. This possibility has created widespread interest in the industry to investigate the feasibility of energy generation. This guide has been compiled to provide information on: the characteristics of poultry litter relevant to energy generation; the types of technology available for energy generation; and the feasibility of generating energy from litter. The main technologies that can be used to generate energy from poultry litter are combustion, gasification/pyrolysis and some forms of anaerobic digestion. Some of these technologies, while promising, have not been developed to the commercial scale. The information in this guide is provided to give a general idea of the suitability of the technology for the chicken meat industry and the likely feasibility of its adoption in the future. Details from the primary research projects that provided information for this guide can be found in a companion literature review, which is available from the RIRDC website. This document is entitled: Grower Options for Spent Litter Utilisation RIRDC project no. PRJ RIRDC Publication no. 14/193 Poultry litter from the grow-out phase of chicken meat production. 7

8 Energy generation technologies There are a number of technologies available for generating energy from chicken litter. Considering the properties of litter (relatively dry, high wood content), thermal processes (combustion; gasification; pyrolysis) may be appropriate. Biological processes (such as anaerobic digestion) may also be suitable with certain processes. Thermal processes Combustion, gasification and pyrolysis are thermal processes that yield different products and are useful for different applications. Of these, combustion is by far the most developed, having been applied for hundreds of years. The product is heat, which can be used to generate electricity. Several commercial combustion power plants are operating in Europe and North America using poultry litter and other animal manures as a feedstock. Gasification is also a reasonably well-understood process, but has not been applied broadly at the commercial level. The product of gasification is a fuel gas, which can be used to generate heat, or directly in an engine to generate electricity. Gasification also generates char, which can be used as an energy source within the process, or sold as a by-product. Pyrolysis as an energy generation technology is still in the development phase. Pyrolysis is similar to gasification, but is controlled to produce gas, bio-oil and biochar. These processes are discussed in detail in the next sections. Anaerobic digestion Anaerobic digestion is a way of breaking down a biomass into gas via a biological process in the absence of oxygen. The product is biogas, which is a mixture of carbon dioxide (CO 2 ) and methane (CH 4 ). This gas is generally used for heating or electricity generation. Anaerobic digestion is best suited to high moisture biomass products that are readily degradable. However, different technologies are available that may be suitable for use with chicken litter. Figure 1. Products and pathways for biochemical and thermal processing of biomass. 8

9 Composition and characteristics of chicken litter Chicken litter is a mixture of bedding material (such as straw, sawdust, wood shavings, rice hulls or straw) and manure. In Australia, meat chicken sheds are generally cleaned out after each batch of chickens and fresh bedding material is placed for the new batch of chickens (referred to as single batch litter). This means the proportion of bedding material to manure is higher than where multiple batches of chickens are raised on the same bedding material (multi-batch litter). It should be noted that a small portion of the industry does reuse litter in this way, and the properties from this multi-batch litter will be different. The litter characteristics referred to in this guide are for single batch litter. The properties of chicken litter will vary depending on the amount of bedding placed in the shed. Estimates suggest that at typical bedding use rates the volatile solids (VS) content of chicken litter is close to: 50% derived from bedding (by mass), and 50% derived from manure. Manure and bedding materials have very different properties for some energy generation processes. For example, the degradability of VS in the manure fraction will be higher in an anaerobic digestion process than the VS from the bedding fraction (particularly for wood based bedding materials). This is a critical factor to consider when assessing technologies. Because the properties of the bedding material are so important for energy generation, if in the future energy systems are adopted, they may require a selection of bedding materials specifically suited for the particular energy generation system installed. Moisture content is an important factor for some energy generation technologies. Chicken litter is quite dry, averaging 20-26% moisture (based on 123 samples of Australian litter). In a survey of Australian litter samples, this varied slightly between types of bedding material (see Table 1). Table 1. Moisture content of spent litter from different bedding materials (average and range) 1. Analysis Straw (n=28) Sawdust (n=26) Wood shavings (n=65) Moisture (%) 20 (15-25) 25 (20-29) 26 (21-31) Dry matter (%) 80 (85-75) 75 (80-71) 74 (79-69) 9

10 Typical poultry housing sheds Ash content is also an important factor for energy generation. Because most Australian chicken litter is single batch, the ash fraction is fairly low (10-12%) in comparison with multi-batch litter. In the USA the majority of chicken litter is multi-batch. This means that the ash content is considerably higher (up to 34%). This reduces the energy potential of the litter. The energy content of chicken litter is a function of the ratio of ash to volatile solids (VS). On a dry basis, Australian chicken litter is expected to have an energy content of around MJ/kg (higher heating value HHV). For thermal energy generation applications (i.e. combustion or gasification), heating value is strongly influenced by the moisture content of the material. Fresh poultry manure is 70-80% moisture and is unsuitable for thermal energy generation processes. However, litter has a much lower moisture content partly because it is a mix with the bedding material, and partly because the chicken sheds use ventilation systems which dry the litter. At moisture levels of around 20%, the heating value of chicken litter is expected to be around 15 MJ/kg. As the ash content and energy content are so important for the potential energy yield that can be extracted from chicken litter, it is vital that these characteristics are quantified before any energy recovery options are explored by Australian meat chicken farmers. Table 2. Summary of estimated content proportions in Australian chicken litter. Estimated Australian chicken litter properties Amount Manure proportion of VS* 50% Bedding proportion of VS 50% Ash content 10-12% Energy content (HHV**) - dry basis *volitile solids **higher heating value MJ/kg Australian single batch chicken litter has relatively low levels of ash and moisture. On a dry basis, the heating value (HHV) is expected to be MJ/kg. For thermal energy generation applications the heating value on an as received basis will be lower because of the moisture content. 10

11 Combustion Direct combustion is the simplest method of generating energy from chicken litter. Combustion involves burning the material in the presence of oxygen to produce heat. This process is used for coal fired electricity generation and has been applied for many waste streams. The process is mature and widely available, and there are several commercial plants using chicken litter as a feedstock in Europe and the USA. The combustion process comprises five main steps: 1. Drying occurs at 100 C. Heat is initially required to evaporate water within the material (chicken litter). 2. Devolatilisation occurs once sufficient temperature has been reached (> 300 C) volatile organic gases within the biomass are released. In addition to this, the chemical bonds in cellulose and lignin are broken down. 3. Gasification occurs at temperatures > 800 C and results in the release of carbon monoxide (CO) and hydrogen (H 2 ) from the gasification of solid char. 4. Char combustion occurs when char is oxidised and converted into carbon dioxide (CO 2 ) and CO gases. 5. Oxidation occurs when volatile gases and tar are converted into heat energy through oxidation at temperatures > 800 C. 6. Chicken litter has relatively low ash and moisture levels compared to many other waste materials, making it a reasonable feedstock for combustion. Chicken litter may also be co-fired along with coal to improve efficiency. The challenges in the combustion of chicken litter relate to problems with fouling and potential production of hazardous gases, and pre-drying may also be required. Ash from combustion of chicken litter may be a valuable by-product because it contains residual phosphorus (P) and potassium (K) (valuable plant nutrients) that could be processed into fertiliser. This has not been investigated in detail, but may improve the economic feasibility of chicken litter combustion in Australia. Figure 2. Direct combustion flow chart showing major outputs from the combustion of biomass such as spent poultry litter 2. 11

12 Feasibility of process The feasibility of combustion for energy generation from chicken litter is limited by: The scale of potential projects, The amount of available litter within an economic transport distance of a facility, and The moisture content of the litter feedstock (which affects the costs of drying the litter prior to combustion). USA studies suggest that the energy potential of combusted chicken litter ranges from 7.9 to 14.6 MJ/ kg as received (wet basis). This gives it an energy potential of around 15 MJ/kg on a dry weight basis. This value is lower than that expected for Australian chicken litter (17-18 MJ/kg) due to the higher ash content of USA litter. These USA studies also give an electrical energy generation potential of chicken litter from combustion between 0.5 and 1.2 kwh/kg (average = 0.8 kwh/kg) on an as received basis. Chicken litter is being successfully combusted to produce electricity at several large plants both in the UK and the USA. These plants are in the medium range of energy generation (8-60 MW), with the newest plants on the larger end of this range (35-60 MW). The technology for generating energy from chicken litter using combustion appears to be the most advanced of all the waste to energy technologies, with many commercial plants either operating or being constructed. Therefore further research and development into the direct combustion of chicken litter should not be required, as many commercial facilities are currently operating or in the planning/construction phase. A standard spark ignition combined heat and power (CHP) biogas generator used to produce electricity and heat. Direct combustion is the simplest and most established method of converting waste to energy. Studies suggest that the energy potential of combusted chicken litter ranges from 7.9 to 14.6 MJ/kg as received. The feasibility of the combustion of chicken litter has been proven on a commercial scale in countries such as the UK, the USA and the Netherlands. 12

13 Gasification Gasification is a thermal process which converts organic materials into a hydrocarbon gas called syngas. Syngas is mainly composed of hydrogen, carbon monoxide, carbon dioxide and methane and can be burnt in a generator or combined heat and power (CHP) unit to produce electricity. One major advantage gasification reportedly has over direct combustion is lower emissions. Gasification may be a suitable technology for energy generation from chicken litter, but few commercial facilities exist anywhere in the world at the present time. The gasification process comprises four main steps: 1. Drying consists of the fuel (e.g. biomass, such as litter) being heated and dried at the top of the gasifier unit. To initialise drying, the temperature in the gasifier must be greater than 150 C to enable the evaporation of water. 2. Pyrolysis occurs when there is no available oxygen, sufficient biomass temperature has been reached (> C) and the organic compounds begin to decompose. The resulting products are a mixture of char, tars and volatile gases. 3. Oxidation occurs when the outputs from the pyrolysis stage react with the char and volatile gases to produce CO 2 and water (H 2 O) in the presence of O 2 at temperatures between 700 and 1,200 C. 4. Reduction occurs once all of the oxygen has been consumed and the gases have undergone a final endothermic reaction. These reactions reduce the temperature of the oxidised gases and convert the H 2 O, CO 2 and the remaining char (carbon) into hydrogen, water, methane and carbon monoxide. Figure 3 shows the four main steps in the gasification process. The char product may be re-used in the process of heating and drying the biomass to improve efficiency. Alternatively, this char could be sold as a by-product. Figure 3. Gasification flow chart showing the major inputs and outputs of the process. 13

14 Feasibility of process The feasibility of gasification for energy generation from chicken litter is limited by the cost of scrubbing the impurities in the syngas and the production of ash and potassium, which leads to the fusion of tar, resulting in increased operating costs for the system. There is however, significant research and development occurring in this area at present and there will likely be further advancements in the technology in the near future. Gasification trials in the USA showed that energy content can be in the order of 6.75 MJ/kg litter (at 25% moisture). Electricity generation rates from poultry litter may be in the order of 0.5 kwh/kg litter. Chicken litter contains high levels of valuable nutrients. While there is less research investigating the value of char from gasification processing, this is an option when using chicken litter as a feedstock. However, this would reduce the energy efficiency of the gasification process because char would not be available as a feedstock. Further research is still required to investigate the properties of char from chicken litter and the economic feasibility of producing char. There are very few commercial gasification projects operating worldwide which utilise chicken litter as a fuel source. While the process appears promising, commercial case studies will be required to give the industry confidence to invest in this technology. BiGchar s fast rotary hearth gasification unit (used to gasify different biomass feedstocks). Gasification converts organic materials into syngas. Syngas is composed of H 2, CO 2, CO and CH 4 and can be burnt in a generator or CHP unit to produce electricity. The energy content of syngas can be in the order of 6.75 MJ/kg litter. The process can also produce a nutrient rich char that can be used as a fertiliser. 14

15 Pyrolysis Pyrolysis is a specialised from of gasification which results in the decomposition of a material by heat in the absence of oxygen. Three primary by-products are created during the pyrolysis process. These are bio-oil, gases (such as methane, ethene and acetylene) and biochar. The main difference from gasification is the absence of oxygen in the process, and the production of oil in addition to gas. Pyrolysis has been the subject of a lot of research, but there are few commercial scale facilities using this technology presently. Pyrolysis can be divided broadly into two types: slow or fast pyrolysis. Slow pyrolysis produces more biochar and less energy, while fast pyrolysis produces more liquid and gas from the same product and less biochar. Fast pyrolysis uses high temperatures, very short contact times and requires small particles sizes (< 2mm). The process of pyrolysis is described in Figure 8. The main energy outputs of pyrolysis are bio-oil and gas. Bio-oil properties vary depending on the feedstock used, and the technology is not well advanced for refining this product. Studies show that the gas produced from pyrolysis has a calorific value of MJ/m 3, and may be used to fuel engines and gas turbines without modification. Specific studies into bio-oil production from the pyrolysis of chicken litter give a heating value of MJ/kg. Feasibility of process The feasibility of pyrolysis for energy generation from chicken litter is limited by the state of the technology, relatively lower energy generation potential of the process, and the requirement for a strong revenue stream from the biochar. As an indication, biochar would need to sell for in excess of $500/t to be feasible. The economic feasibility also often requires a revenue stream for treating the feedstock material (i.e. gate fees). As chicken litter is a saleable product, feedstock will be a cost to the process, rather than a source of revenue. Figure 4. Schematic diagram of a typical plant set-up 4. Small-scale pyrolysis plant operated by Pacific Pyrolysis in NSW (photograph courtesy of Adriana Downie 15

16 Biochar Biochar can be an output from the gasification or pyrolysis process. Biochar from chicken litter is a nutrient rich, stabilised carbonaceous soil conditioner. This is an attractive option for recovering the nutrient value from chicken litter in addition to the energy value. The P and K in one dry tonne of chicken litter are valued at $62* when compared with Biochar can be produced as a coproduct from gasification or pyrolysis. Biochar from chicken litter may be a valuable soil amendment and fertiliser product with multiple benefits for users. synthetic fertilisers. Provided biochar can provide nutrients in a concentrated, plant available form, this may substantially increase the value of the product. Several Australian research projects have shown chicken litter biochar to be a valuable fertiliser, which is promising. Biochar has also been promoted as a means for improving soil health and structure, moisture and nutrient retention. Biochar may also be a means to sequester carbon and may be eligible for carbon credits under the Emission reduction fund in the future. However, this is subject to further research. The main barrier to biochar manufacture is the high cost of production, meaning biochar needs to retail for at least $500/tonne to be economically viable. Presently there are limited markets available for biochar at large volumes. Biochar produced during pyrolysis 16

17 Anaerobic digestion Anaerobic digestion is a biological process for generating energy from biomass such as chicken litter. The process is ideal for wet materials, but can also be used for solids such as poultry litter, with appropriate technology. Anaerobic digestion produces biogas, a mixture of carbon dioxide and methane which has an energy value of around MJ/m 3. Using anaerobic digestion with animal manure also results in a nutrient rich effluent and solid material. While anaerobic digestion is a mature technology that has been broadly applied worldwide, it has only infrequently been used for chicken litter. This is because litter is generally quite dry and has high levels of nitrogen, which can inhibit digestion. The bedding material present in litter is also not highly digestible, particularly in systems with a short hydraulic retention time. One approach for digesting a high solids content material such as chicken litter is to use a solid phase leach bed system (Figure 5). However, this technology is still in the research phase for use with chicken litter in Australia. Solid phase leach bed digestion can be either batch (where the system is reacted until no more methane is produced) or continuous (where material is continually added, and spent material is removed). The material goes through theanaerobic digestion process in dry mode (i.e. total solids content of 30-40%). Leachate from the system is recirculated through the digester to promote biogas production. Because of the ammonia inhibition process, single stage solid phase leach bed systems are not likely to be suitable. A more suitable approach would be to combine the leach bed with a high-rate anaerobic digester (generally upflow-anaerobic sludge blanket) and combined side-stream ammonia removal. This process relies on a high proportion of the volatiles dissolving in the leachate. As yet, the process has not been tested with chicken litter. Figure 5. Combined leach bed and high-rate anaerobic system for poultry litter. Biogas plant in Denmark 17

18 Feasibility of process The feasibility of anaerobic digestion for chicken litter has not been investigated at the commercial scale. There are a number of practical considerations in addition to economic considerations that must be taken into account. Firstly, anaerobic digestion requires water and generates a liquid effluent stream which may be difficult to manage. It may be different to set up such a process on farms in closely settled areas. Economic feasibility is likely to be limited by the energy yield (governed by the digestibility of the material and the retention time), capital costs of set up and the potential for recovering nutrients from the effluent as a high value fertiliser. These factors are subject to a high degree of uncertainty. The Figure 6 shows the payback period based on three digestibility rates. Assuming 30% digestibility, the payback would be in the order of 14 years for a large farm. Figure 6. Payback period dependent on digestibility. 4 Figure 7. Anaerobic digestion technologies compared. 4 The solid phase leach bed system is suited for a high solids concentration and has long hydraulic retention times. 18

19 Unlike other intensive animal industries such as pork, anaerobic digestion of chicken litter will not provide a significant revenue stream from carbon credits. This is because litter is not a large source of emissions under current management practices, so the abatement potential is low. Anaerobic digestion is a biological process for generating biogas (a mixture of methane and carbon dioxide) from biomass. This biogas has an energy value of around MJ/m 3. New technologies may make anaerobic digestion possible with chicken litter provided manure digestibility is sufficient. Research is ongoing in this area. 19

20 Summary The future of energy generation from chicken litter. Bio-energy generation is the topic of large amounts of research globally, and new innovations are leading to constant technological improvements. Interested parties are encouraged to conduct their own investigation into advances in the technology. The feasibility of energy generation can also change substantially with changing electricity costs, regulations and opportunities for new revenue streams from mitigating greenhouse gas (GHG) or from the sale of fertiliser. At the time of writing, options to generate revenue from manufactured fertiliser or mitigation of GHG look promising, but further progress may need to occur before these revenue streams can be relied on. Feasibility at the project scale will also depend on specific considerations such as on-site power costs and the specific characteristics of chicken litter available. Interested parties are encouraged to conduct site-specific assessments rather than relying on the general feasibility presented here. Review of the feasibility of energy generation projects is recommended when substantial changes to technology, costs or revenue opportunities change. References 1. Craddock, T & Hollitt, J 2010, Piloting chicken litter usage in broadacre cropping - Setting research directions, Rural Industries Research and Development Corporation, Canberra. 2. Nussbaumer, T 2003, Combustion and co-combustion of biomass: Fundamentals, technologies, and primary measures for emission reduction, Energy & Fuels, 200 (17), Laird, DA, Brown, RC, Amonette, JE & Lehmann, J 2009, Review of the pyrolysis platform for coproducing bio-oil and biochar, Biofuels, Bioproducts and Biorefining, 3 (5), McGahan, E, Barker, S, Poad, G, Wiedemann, S & Batstone, D 2010, Conversion of waste to energy in the chicken meat industry - Final Report, RIRDC Project No PRJ , 21 December, 2010, Rural Industries Research and Development Corporation, Canberra. Acknowledgements: The Authors would like to thank the many researchers who have completed the detailed research that underpins this guide for the RIRDC over the last 10 years. This research is summarised and referenced in full in the accompanying report for this project, available from the RIRDC: 20 Wiedemann, SG, Bielefeld, EN, McGahan, EJ, Valentine, JG and Murphy, CM 2012, Grower Options for Spent Litter Utilisation User Guide Development Final Report, RIRDC Project No PRJ The Rural Industries Research and Development Corporation Chicken Meat Program, funded this guideline.

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22 Energy Recovery from Litter: A Guide for Users by S.G. Wiedemann of FSA Consulting Pub. No. 14/096 Phone: Fax: Bookshop: Postal Address: Street Address: rirdc@rirdc.gov.au PO Box 4776 Kingston ACT 2604 Level 2, 15 National Circuit, Barton ACT