Primitivism and the Vernacular Technical Report David Masters AEE4
An investigation into the On-Site production of Bio-Gas to meet the Folk Factory’s heating demand.
Primitivism and the Vernacular David Masters 10016634
Report Summary This investigation looks into the production of Bio-Gas through anaerobic digestion to fuel a CHP and Boiler setup in the Folk Factory. The CHP and Boiler plant will be sized to meet all space heating demand within the factory along with DHW services and heater battery loads on the Air Handling plant. The report also considers the contentious issues involved with anaerobic digestion in an urban environment and outlines delivery procedures and site masterplanning to optimise the efficient running of the digester. The main driver for the project is reintroducing the tradition of the region whereby farms serve there local communities. The folk factory not only produces food from the restaurant on site, but also provides to local businesses within Bath and runs alongside the Bath Farmers Market (the first farmers market in the UK). Animal waste, food waste and composting hayleige will be imported in locally from surrounding farms and restaurants to fill the digester and the digestate will be used on site for plant fertilizer and also redistributed locally for gardening compost. Human waste will not be used in the folk factory digester.
CONTENTS Introduction.......................................................................................................................................................................................3 Specification of the building............................................................................................................................................................4 Factory heating strategy...................................................................................................................................................................5 Summary of Literature.....................................................................................................................................................................6 Promoting a Small Scale Anaerobic Digestion System................................................................................................................7 Industrial Heritage of Locality........................................................................................................................................................9 Determining required load............................................................................................................................................................11 Sizing Boiler and CHP plant.........................................................................................................................................................13 Determining annual fuel demand................................................................................................................................................19 Sizing the Digester..........................................................................................................................................................................23 Incentives.........................................................................................................................................................................................25 Contentious Issues..........................................................................................................................................................................27 Delivery Strategy ............................................................................................................................................................................29 Conclusion.......................................................................................................................................................................................32 Reference List...................................................................................................................................................................................33 Bibliography.....................................................................................................................................................................................34
1
Anaerobic Digestion
Biogas piped to Folk factory plant room and boilers
Purifier and Compressor
Anaerobic digestion is the natural process where micro-organisms break down organic matter, in the absence of oxygen, into bio-gas. Bio-gas is a mixture of carbon dioxide (CO2 ) , methane and digestate (a nitrogen rich fertilizer). “The bio-gas can be used directly in engines for Combined Heat and Power (CHP), burned to produce heat and electricity.” (DEFRA, 2013).
Biogas purification and compression warehouse
Anaerobic Digestion is not a new technology, it has been widely used in the UK for the treatment of sewage for over 100 years (DECC 2011). Only fairly recently has it been used for treating other waste such as crops and food waste. For the purpose of this investigation, input products for the digester will only be food and crop waste sourced locally and animal waste from local farms. No human waste is used. Many forms of biomass are suitable for AD; including food waste, slurry and manure, as well as crops and crop residues. However, woody biomass cannot be used in AD because the micro-organisms can’t breakdown the lignin, the compound that gives wood its strength.
Digestate removed for compost and fertilizer
Foundations and retaining walls water tight
Bio-gas
Decomposing matter
Shredder
Animal waste and organic waste delivery
AD is not a new technology, it has been used in the UK since the late 1800s, but now an increasing number of AD plants are being built in the UK to generate clean renewable energy. AD is also used to treat the waste produced in homes, farms, supermarkets and industries across the UK. This helps divert waste from landfill. (Biogas-Info) The folk theatre project is an attempt to realise a sustainable initiative which is based on past traditions. In sourcing, producing and distributing locally, this cuts out the emissions from transport and supports local businesses. The use of the AD plant supports the overall narrative of the Folk Theatre project.
2
Introduction
The Folk factory building type has been specified as a warehouse / factory with radiant heating with support from radiators and UFH being the chosen method of heating due to the fact that the temperature of the space need not be high as it is an active environment. To maintain adequate comfort conditions a controllable heating system will be necessary so automatic PID controls will be installed. The PID controls will maintain room temperature around a steady level at the set-point controlled by temperature sensors within the space (around 21oc). When heat gain from occupant activity and factory and bakery operations increases the temperature of the room above the set-point, the heating medium is regulated down steadily so there is no over or undershoot in the temperature control. Radiant heating is not always achievable but radiators produce about 70% convective and 30% radiant heating. As purely radiant systems are difficult to control at a set-point, convective radiator systems will be incorporated under windows to reduce cold draughts. Underfloor heating will be laid in office spaces, the bakery and folk music studios. Not on the warehouse floor. Other spaces will be supplied heat through wall mounted radiators and conditioned air from ceiling mounted fan coil units. The 1st floor of the folk factory includes the A-Frame roof-space within its volume and consequently heat is lost into the roof-space of the factory. Fans will be installed in the roof-space to keep warm air down with the occupants. (See model image above for clarity of room volume).
3
Digester Location
Folk Factory
AD Plant Building
Mains Water Electrical Line
Specification of Building The folk factory wing is very open plan in its layout. Using regional vernacular precedent to inform building materiality, the factory (ground floor) has 400mm thick concrete walls ‘referred to as dung-walling’. The concrete walls were chosen for there thermal mass properties so heat gains are reduced during working times due to the decrement factor of the walls. Typically farm buildings were constructed of stone and created cool internal environments. As the infiltration rate is high on the first floor, a lightweight shell was designed to reduce the buildings total embodied carbon. Cross ventilation can occur on the first floor allowing for fresh air movement through the folk music studio spaces.
Justification for using a mixture of radiant, convective and underfloor heating systems is due to the carbon emissions linked with running a VAV system for example for air heating. An Ecotect model confirmed that a VAV system would be less efficient due to the occupancy behaviour and variation of spaces within the factory. Coupled with a fan coil system for cooling, the proposed heating strategy was decided.
Deep eaves shade the windows on the south facade reducing heat gains through direct sunlight. All roof-lights are positioned on the north facade to allow ambient light into the studio spaces.
4
Factory Heating Strategy
The first floor folk music school and potting shed will be heated using radiator and air systems. The boiler will be sized to accommodate heater battery load on the primary Air Handling plant. Perimeter radiators will be positioned under windows and within studio zones. The potting shed will use the air system due to the environment it needs to create for plant potting and germination. The ground floor is predominantly open plan factory / warehouse space with a range of different activities. The space has limited windows although the 3 light tube chimneys provide diffuse light into the space. Radiant heating will be used in the form of radiant panels and perimeter radiators and underfloor pipework in the offices, butchers and bakery. Fan coil units will provide conditioned air. The basement space will be heated through underfloor heating. The food stores will be conditioned with split unit systems. There is minimal air infiltration to this space. The basement will naturally remain cool due to no solar gains and minimal occupancy gains. Also it houses plant rooms and food stores so the need for heating is minimal.
5
Summary of Literature
A significant amount of literature on the topic of anaerobic digestion covers the digestion of ‘sludge waste’ and there is little content on the digestion of the organic matter such as waste foods. Sludge waste can be defined as animal slurries and human waste. Performance Summary for Anaerobic Digestion of Dairy Cow Slurry at AFBI Hillsborough. This report summarizes a 27 month intensive monitoring procedure of an Anaerobic Digester plant installed on a dairy farm at Hillsborough. This document provides information on the gross calorific value of differing fuels for the anaerobic digester and is a vital report in the production of this study. Biogas Technology by B.T. Nijaguna This book outlines the fertilizer value for different types of biogas manure and is the source for the section of the technical report which looks at digester output. Anaerobic Digestion Strategy and Action Plan This source provided jointly by DEFRA and the DECC outlines the process of an anaerobic digestion strategy and provides information on the contentious issues involved.
A number of other documents including ‘How to design a heating system’ by CIBSE are looked at for the sizing of plant. Primary energy production of Biogas in Europe 2007 (Sourced from European Union)
It was found that the UK is the second largest producer of Biogas in Europe which is encouraging for this report.
6
Promoting a Small Scale Anaerobic Digestion System It is important for this study to promote the use of AD. As there are a lot of contentious issues surrounding the technology, (especially in urban environments) a technical report for a proposed building needs to show how the technology fits into the building program. It has already been suggested the principles behind the choice of this technology.
Labour requirements for waste treatment at Hillsborough AD plant.
Initial downsides to be addressed with the technology; Management of organic wastes involve considerable expenses in collection, treatment and disposal (see illustration 1).
To ensure this is not an issue, better management of the system must be employed. - A change of mentality of people involved in relation to wastes - An evolution in attitude on use of natural resources - Implementation of more efficient waste separation procedures
Illustration 1
Anaerobic digestion has a number of advantages such as; - Renewable energy production - Waste treatment - Better greenhouse gas emission - Fertilizer production (Lisbon Research Team) 2009 A large scale AD plant was approved planning permission in Wheldrake, Yorkshire. With suitable landscaping and sensible design of scale, an AD plant should fit into the city context. Especially as just across the river from the Avon Street site used to sit a substantial Gas works.
7
Initially AD was only applied as a single substrate technology, meaning it only digested 1 type of waste instead of a mixture due to better output. Although it has been shown in numerous reports (Carbon Trust and DECC) that co-digestion is just as effective. The co-digestion process includes advantages such as; - Less expensive - Allows more efficient preparation of digester feedstocks - Increases the scale of the system (depends on planning) - Can improve degradation efficiency resulting in higher gas yield - Compared to separate substrate technology, co-digestion reduces investment and ecological footprint - Reduces greenhouse effect “Co-digesting other organic materials along with slurry can greatly increase biogas yield per unit volume of digester. For example, by adding 3 tonnes grass silage with the slurry, the AFBI digester could, in theory, more than double biogas production.� (Frost and Gilkinson, 2011)
Co-digestion AD potential feedstocks from Bath region
With the co-digestion AD setup, a number of different wastes from around the city of Bath and local region can be used. In order to process all food wastes that are delivered to the AD plant, an adjoining building has been masterplanned on the site to link to the plant. This building also holds machinery for purifying and compressing the biogas which is used in the folk factories CHP and boiler plant.
8
Industrial Heritage of Locality
Due to the contentious issues involved with AD such as waste delivery, a look at the Industrial heritage of Bath in order for the AD project to be accepted by Bath city planning authority is necessary. The site sits directly opposite Buro Happolds Engineering office which was once a warehouse that dealt with deliveries down the river Avon from Bristol and beyond. The crane housings can still be seen on the faรงades for lifting cargo of the canal barges. Also up the river about 500 meters from the site is the old Bath city gasworks and industrial warehouses.
Industrial hub of the city of Bath. Picture sourced from Bath in Time
It is due to this industrial heritage that surrounds the project site that an AD plant may have the potential to be approved.
Folk Theatre site 500 meters away.
9
Addressing potential threats to project proposal From research of planning policies, very little was found on heritage when it comes to waste management planning applications although this should be addressed. The project is in-keeping with the history of the site and to support a sustainable opportunity such as AD is important in the current climate.
Pictures sourced from Bath in Time of Bath Gasworks
Planning for Sustainable Waste Management (Planning Policy Statement 10). PPS10 states that waste planning authorities should take into account the likely impact on the local environment and on amenity when considering planning applications for waste management facilities. Annex E provides a list of locational criteria against which suitable sites shall be tested, the criteria includes environmental and amenity issues such as visual intrusion, traffic and access, air quality and noise. The WLP principles for waste development (Policy 1), includes minimising the transportation of waste from its source; providing the Best Practicable Environmental Option (BPEO) for the waste stream; and the minimisation of harm to the environment, human health, natural resources, local amenity and highway safety. The project does encourage the importation of local waste products and this should not be an issue. It has been discussed above that the site’s close proximity to urban areas and the communities it serves, provides fundamental support for the proposed development. In terms of Environmental affects. PPS10 may suggest a rural location with good transport links is preferable, consequently reducing vehicle movements within the city.
10
Determining Required Load The anaerobic digester will be sized to meet the heating requirements of the folk factory which is the ground floor of the wing building, and the folk music studios and potting shed on the 1st floor. To determine the required heating load firstly it must be considered that the digester plant needs a heat exchange flow through it. This heat load should maintain an optimum digester temperature of 35oc to 40oc for the digestion process to work. (Frost and Gilkinson, 2011). Along with the load for the digester, the heating coil load for the air handling plant of the factory must be added along with domestic hot water (DHW) duties, heat losses from the fabric and ventilation and lastly a +20% margin. The 20% margin was decided based on CIBSE guide F (2002) section 10.1.2.2 and BSRIA Guidance Note 12/97 Oversized Heating Plant. BSRIA Guidance Note 12/97 states that it is useful to add a margin when sizing boiler plant for 4 main reasons; - In case of future extension - Quick heat up when the system is cold - In-case of mistakes in heat loss calculations - Loss of efficiency later in boiler life
All calculations were performed manually following relevant CIBSE and BSRIA guides although an ecotect model was produced to back up those calculations. The ecotect calculations did not match the manual calculations and this was due to an error in the model for the ground floor and basement. A ground line was not added at ground level and the model sits a storey higher than it should. This caused errors with partition adjacencies. 11
Heat Loss through Fabric and Ventilation
DHW Load
Firstly the ventilation conductance was calculated;
The domestic hot water load for the factory and folk school studios is designed following CIBSE Guide G (Public Health Engineering) 2004. Section 2 states that typically 40 litres of hot sanitary water is allowed per day per person within a working building. The space has a design human capacity of 60 therefore the factory requires 2400 litres of heated water per day at a flow temperature of 60oc or above to mitigate leigionella. Mixing valves will be installed at each outlet.
from table 5.2 in CIBSE Guide A the air change rate (N) for the factory and studios is 3. The volume of the space was calculated to be 6900m3 this gave a ventilation conductance of (3x6900/3) = 6900
Boiler power for DHW; R = 0.5 for radiant system from table 5.4 CIBSE Guide A F1CU = 1.063
Other hot water services
Cold service
= m x Cp x (thot - tcold ) x hours heat up x efficiency x 3600 Typical boiler efficiency = 80% Hours heat up (sporadic) = 1.5 hrs =2400 x 4.187 x (60-10) x 1.5 x 0.8 x3600
F2CU = 0.811
= 103.4 kW
Mixing valves Showers in Factory
Total heat loss is given by equation,
Room condition = 21oc Outside air condition = -4oc Total heat loss through fabric = 178.94kW
Hot water calorifier
M Infiltration heat loss (Qv)
Cold water storage (Short time)
Mains water supply
B
Room condition = 21oc Outside air condition = -4oc Qv = 1/3 x 0.077 x 6900 x 25 Qv = 4427.5 W = 4.5kW
Boiler Expansion vessel
12
Selected Plant
When all loads and the building heat loss are added together, the overall boiler load required equals 398.808 kW. As the 20% margin has already been added, 2 boilers sized to meet 400kW of output is sufficient. CIBSE Guide B1 (2002) section 4.7 gives details on the Plant Size Ratio (PSR). The PSR of the factory = 2.228. The optimum plant size ratio is a compromise between the following factors; - Occupancy pattern - pre-heat time - thermal response of building - greater capital cost and maintenance cost - stability of controls - seasonal efficiency
AHU load calculated from benchmark assumption from BSRIA Guidance Note 12/97 Digester load taken from Action Plan document published by DEFRA
13
Both heating plant are selected Hoval units. These units have been selected as they can be adapted to run on Bio-gas. CHP unit - Hoval Powerbloc CHP EG-140 Boiler Plant - Hoval UltraGas 250
14
Micro-generation on-site (CHP) The risks of climate change are now accepted and the need to reduce cumulative CO2 emissions has become a fundamental part of energy policies. The UK climate change act has set a legally binding requirement for an 80% reduction in CO2 from 1990 levels by 2050 under the Kyoto protocol. (Climate Change Act, 2008) The committee on climate change 2010 states that approximately 16% of total CO2 emissions are from the supply of heat for space heating and hot water in buildings. CHP (Combined Heat and Power) has been recognised as a technology that can reduce CO2 emissions. The Carbon Trust conducted a field study and showed that over the course of a year, Internal Combustion engine Micro-CHP units saved between 12-21% in CO2 emissions compared to conventional separate heat and power generation. CTC788 (2011) The UK has benefited from indigenous fuels for energy generation such as coal, oil and natural gas (coal in particular). Although as these resources are diminishing the UK is increasingly importing fossil fuels which are increasing in price due to worldwide demand. Energy security is essential with a potential for gas supply interruptions for example. A CHP scheme would consequently require a secure gas supply contract so gas interruptions don’t affect engine performance and onsite electricity generation. The integration of the CHP scheme connected to an on-site anaerobic digester limits the issues with gas supply although digester fuel will constantly need to be filled up. During the summer months when heating load drops, the CHP plant can still produce electricity for on site small power or that power can be distributed to the grid for a Feed in Tariff rate. It is possible with a CHP scheme to also benefit from the RHI (Renewable Heat Incentive) if the size of the plant is small and not sized for district heating purposes. To qualify for the RHI a CHP scheme must pass Good Quality CHP criteria (CHPQA).
This illustration published by CIBSE AM12 shows the energy challenges faced.
15
The energy efficiency of CHP (Carbon Trust 2004)
Since the output of a CHP system will only rarely be able to match exactly the electrical and heating demands of a building, an operational scheme must be decided upon. There are three options, heat-led operation, electricity-led operation, or a combination of the two. Beith (2011). For the purpose of this study, heat-led operation will be used due to the heat to power ratio of the building (1:1.4) determined by a building Ecotect model and also manual calculations. Due to the high amount of electrical requirements in the factory for machinery, lighting and other ancillaries a heat led scheme has been decided on. If the CHP unit was sized to meet the electrical base load, then it’s potential heat output would be too much for the building to utilize and significant heat dumping would take place. Also a gas engine CHP unit was specified for the building and if the heat to power ration was greater than 1:1.5, a gas turbine would have had to be used. This would have resulted in greater capital expense in CHP plant and a larger anaerobic digester. (CTV044) Despite there lower efficiencies, piston engines are popular because of there lower capital cost than gas turbines. Also there is a considerable ease of maintenance for an IC (Internal combustion) engine as CHP unit engines are generally retrofit lorry engines. IC engines can be significantly affected by biogas with a high siloxane content. It is generally human waste which contains high levels of silicon which abrases the combustion engine workings. This study does not look at digesting human waste. (Parker 2009)
Spark ignition IC engine running on biogas. (Ener-G, www.energ.co.uk)
The anticipated running hours for the CHP unit are between 06:00 am and 20:00 pm. On a weekday in september the gas base heat load can be found to size the CHP plant. The base gas load is 17.5kWth and the electrical base load is 20kWe. Hoval Powerbloc = 90% efficient Therefore actual base heat load = 17.5 x 0.9 = 15.75kWth
Ecotect Data
16
Energy Balance
Annual Efficiency Electricity out 140kW
Gas in 414.6 kW
140 kWe CHP
1,949,117.52kWh
Heat out 207kW
Reliability and availability of the CHP unit are important issues. As CHP must run continuously for extended periods to achieve best economic returns, the availability of the unit must be high. (DECC) When discussing CHP availability for the Hoval unit, Griffiths states that the maximum temperature which can be produced from a particular energy source (gas engine) is a key factor in determining the amount of work that can be generated from that source. The potential of the gas engine to undertake work is termed availability. Availability is expressed with the following equation; A = Q(T1-T2)/T1 Where Q =Energy content of heat source, T1 = Temperature produced by heat source, and T2 = Ambient temperature For this study the CHP unit has been sized to meet the base load for September (end of summer) so the unit is sized to run for as long as possible producing usable heat and electricity. - The plant has an availability of 92% - Efficiency of the backup boiler = 90% The plant will run for (14hrs a day × 365 days per year × 0.92(availability)) = 4701.2 hours a year. Carbon Trust (CTV044) states that CHP should run for 4500 hours a year to make the project economical. 17
658,168 kWh
140 kWe CHP
Power Efficiency = 658,168/1,949,117.52 = 34% Heat Efficiency = 1,081,276/1,949,117.52 = 55.5%
1,081,276 kWh
Overall Efficiency = 89.5%
Electrical efficiency is of key importance in all CHP engines. However, Beith (p.134) states “effective recovery of waste heat is also critical in order to provide a good total utilisation of the fuel energy.” For naturally gas fired CHP systems running with a condensing boiler, heat recovery from the exhaust steam can be performed using condensing heat exchangers to recover the latent heat from the steam. The use of a condensing boiler is limited to natural gas fired CHP due to corrosion of the condensing exchangers with other fuels such as oil. Beith (2011). Like a car engine, the CHP engine requires cooling. The heat rejected from the engine jacket and lubricating oil cooling systems is recovered to water circuits using conventional plate heat exchangers. Griffiths (1995. p.66) claims that “virtually 100% of the heat rejected by an IC engine to the jacket cooling water and oil cooling systems can be recovered in practice.” To meet Good Quality CHP criteria, the CHP has to have; - A power efficiency greater than or equal to 20% - A quality index greater than or equal to 105 The quality index for reciprocating engines is; QI = (200×Power Efficiency) + (125×Heat Efficiency) QI = (200×0.34) + (125×0.555) QI = 137.38 Therefore the Hoval CHP unit meets CHPQA criteria and is eligible for climate change levies.
Illustration produced by DEFRA for potential Bio-Waste usage
18
Determining Annual Fuel Demand Anaerobic digestion of animal slurries sourced from local dairy and FABBL farms involves bacteriological breakdown of organic matter to produce biogas and digested effluent (digestate). From the Hillsborough report, it was found that digestate had lower pollution potential, has less odour, contains fewer viable weed seeds, has fewer pathogens than input slurry and is an excellent biofertiliser.
Biogas is a mixture of gases: methane (50-75%); carbon dioxide (25-50%); nitrogen (0-10%); hydrogen (0-1%); hydrogen sulphide (0-1%); and oxygen (0-2%). (Frost and Gilkinson 2011) The calorific value of biogas is variable (depending on methane content) at 20-26MJ/m3 (5.6-5.7 kWh/m3). “The heating oil equivalent is approximately 0.5-0.7 litres oil / m3 biogas.� (Parker, 2009). From these figures it can be seen that biogas is an excellent source of renewable energy.
Weed seeds are an issue when it comes to farmers fertilising there fields with animal slurries. There is potential for small FABBL farms, when purchasing hayleige from other farms with a weed problem, for there animals to spread weed seeds through there dung.
The total solids content in digester feedstocks is important to monitor for efficient running of plant. DEFRA state that a regular supply of slurry for instance, with a total solids content greater than 6%, produces a biogas yield of around 16-20m3 of biogas per tonne of slurry. Therefore it should be noted that excessive dilution of slurry should be avoided. This could be an issue on many farms as cold weather or high water content in hayleige for cattle feed can produce highly diluted slurry. Therefore a capital expenditure and/or civil works on site could incur at the cost of the farmer.
Potential weeds in the UK climate include dock leaves, thistles and nettles.
On the other end of the scale, a high total solids content in slurry of ( > 12%) makes for poor flow characteristics and for difficult pumping in the AD plant.
GCV = 5.6-5.7 kWh/m3
19
GCV = 26.4-26.8 kWh/m3
GCV = 2.5-2.8 kWh/m3 Based on data from www.dti.gov.uk
This graphic shows all AD plant within the UK. It can be seen that 7 On or Off Farm plant are located within the Wiltshire and Somerset region close to Bath.
From the Hillsborough report, it was found that on average over the 27 month period, 1m3 (1 tonne) of slurry at 69g/kg dry matter fed to the digester produced 0.989 m3 (0.989 tonnes) of digestate containing 55 g/kg dry matter, plus 15.2 m3 of biogas with a gross energy value of 85 kWh. The digestate recovered is a much better fertilizer for ARABLE crops for instance as it contains most of the nutrient constituents of the original feedstock but in a reduced chemical form which is more easily uptaken by crops. The mixture of wastes achieved through co-digestion (animal slurries + food wastes) can provide optimal carbon/nitrogen ratios. The higher the nitrogen content, the better the fertiliser.
The digestion process requires a heat input so a certain value of overall energy in kWh produced from digester goes into the running of a boiler to heat digestate. The average digester temperature should be around 37oc. In the case of the Hillsborough report, this amounted to 39% of total biogas energy produced. Along with this, an average electricity demand is required to run pumps and mixers for instance. An anaerobic digester plant typically comprises - a digester tank - buildings to house ancillary equipment (generators, biogas storage tank) - a flare stack (3 - 10m high) - associated pipework - compressor - purifier The size of the scheme can vary in scale from small schemes treating waste from an individual farm through to medium scale schemes dealing with waste from several farms and large industrial plant treating MSW (municipal solid waste). The folk factory scheme falls into the medium category.
20
The plant requires 8429200 MJ of energy per year to run based on Ecotect weather data and degree day assumptions.
From calculations of annual energy input for the proposed plant, it was found that a total of 8429200 MJ or 2357778 kWh of biogas fuel is required to run plant for the proposed hours run time per year. The CHP unit is scheduled to run for 4701.2 hrs a year whilst the backup boiler is scheduled to run for 2184 hrs a year. Based on the Hillsborough report figures, this would mean that if digester fuels using co-digestion achieve 145 kWh/tonne of feedstock, the folk factory digester would require 16260.5 tonnes of feedstock per year. Also on the basis that when compared with the volume of slurry fed, the volume of digestate recovered was almost the same (99%), this would mean that 32358.4 tonnes of feedstock and recovered digestate would have to be delivered and removed from site a year. The amount of deliveries would be more significant during the winter months and this is beneficial to farmers as animals are normally housed during winter meaning slurry removal is required more than in summer.
21
Lower Reule farm digester above is a family run plant. Their AD plant takes in food wastes from local authority collections and commercial food production outfits. The AD plant generates biogas for use on the farm aswell as digestate for fertiliser. The scheme is similar in scale to the Folk factory scheme and is thus a good case study to compare. The digester tank is of a similar scale to the proposed tank in the Folk scheme although the tank will be sunk in a recessed pit in the project so it is not so visually shocking. (See illustration across the page. Lower Reule farm plant was awarded funding of £750,000 from WRAP’s (Waste and Resources Action Program) capital grant scheme.
Preparation of waste delivered to site takes place within the adjacent ancillary building
Ground level
Biogas piped to Folk factory plant room and boilers
Purifier and Compressor
Biogas purification and compression warehouse
The ‘waste hierarchy’ produced by DEFRA ranks waste management options according to whats best for the environment.
Digestate removed for compost and fertilizer
Foundations and retaining walls water tight
Bio-gas
Shredder
Animal waste and organic waste delivery
Decomposing matter
Recessed pit
22
Sizing the Digester
The flow chart shows the process for 1 tonne of animal slurry on the case study report on Hillsborough farm. There are differences in digester performance from summer to winter. The average temperature of slurry used in summer months (June-August) is around 16.4oc (DEFRA). While the corresponding figure for winter months (December-February) is around 6.5oc. The digester typically performs better in summer and this could be due to the higher storage temperatures in the tank encouraging the first step in the digestion process (hydrolysis). This assumption is backed up by Frost and Gilkinson who say, “Slurry temperature and thus energy required for heating was found to be highly correlated with ambient temperature.�
23
Details of AD plant for the Folk Factory Digester tank . Feedstock tank . Digestate store Digester Feed Digester heating . Feed shredder
251 m3 below ground sealed epoxy coated steel tank with 100mm mineral wool insulation and 1mm plastic coated steel outer protection. The tank is continuously stirred. 50 m3 housed in ancillary building with access for delivery of feedstock. Epoxy coated open top steel tank (Housing is sufficiently ventilated with gaps in vertical cladding so odours from feedstock don’t build up.) 50 m3 steel tank covered. Short time storage as delivery and removal scheme will be optimised Fed from feedstock tank with positive displacement lobe pump On site 200kW Hoval boiler connected to heat exchanger within tank supplying flow temperatures of 50oc maintain digester temperature of 37.1oc All digester inputs macerated to a nominal particle size of 12mm
System controller
Programmable logic controller (PLC)
Supplying
Hoval 207kW Biogas boiler Hoval 200kW Powerbloc CHP
To run the Folk factory heating plant which in turn, runs the digester, a total of 44 tonnes of feedstock should be delivered on average per day which is substantial. The level of digestate within the tank should remain at a level and an overflow tank incorporated if feedstock input is greater than digestate output.
CHP
Potential plant size. This AD scheme is a 500 kWe plant which is a similar scale to proposed plant
Short Term Storage 24
Incentives There are a number of incentives for the implementation of an Anaerobic digestion scheme.
Renewables Obligation (RO); The RO provides financial support to generators of renewable electricity. This is done through the incorporation of a biogas CHP unit. AD is in the top banding at 2 ROCs/MWh (Renewables Obligation Certificates per megawatt hour). Other renewable technologies which the RO supports include wind, solar and micro-generation.
Renewable Transport Fuel Obligation (RTFO) The RTFO obliges fossil fuel suppliers to produce evidence that a specified percentage of there fuels for road transport in the UK comes from renewable sources. This can include the use of bio-methane as a road transport fuel. Biofuel suppliers are awarded Renewable Transport Fuel Certificates (RTFCs) for the volume of renewable fuel they supply. This could be a potential for the Folk factory plant if summer demand for fuel is low.
25
Feed inTariffs (FiT)
Renewable Heat Incentive (RHI)
The FiT scheme went live on April 2010 and aims to encourage deployment of additional low carbon electricity generation. This ‘clean energy cashback’ will allow many people to invest in small-scale low carbon electricity, in return for a guaranteed payment both for the electricity they generate and export. Many farms in Cornwall during 2013 installed wind turbines for renewable energy generation. The wind turbine schemes are generally funded by a company who receive a portion of the tariff or exported energy whilst the landowner receives a FiT for essentially renting the land to a turbine. Due to tariff rates dropping for wind turbines on April 2014, this is what provoked significant wind turbine applications during 2013 as the rates remain the same if installed before the drop. Like AD, wind turbines must undergo a planning application before consent is given to start the scheme.
AD receives the long term financial support for renewable heat installations. The RHI is a Government environmental programme that provides financial incentives to increase the uptake of renewable heat. Under the Scheme Regulations 2011, Ofgem have the function of adjusting the RHI tariffs by the percentage increase or decrease in the RPI from the previous calendar year. The current tariff rate for medium commercial schemes with an output of 200kWth - 1MWth is 5.3 p/kWh and with the RPI adjustment is 5.4 p/kWh.
AD plants are currently eligible for a tariff rate of 11.22p per kWh for installed capacity of 500kW or less which is where the proposed scheme lies. An additional 3.1p/kWh is paid for electricity exported to the national grid. Role of Biogas in Renewable Energy Field. Net energy output.
AD Plant connects to factory plant room in the basement.
26
Contentious Issues The site sits within the city heart. Delivery of the feedstocks for the digester must be delivered safely and cleanly. Surrounding the Northern boundary of the site is a college, and student and social housing. With Residencies within this closer proximity to the plant, complaints will arise. The masterplanning of the site aims to minimise visual and air quality issues. The planting of an orchard and permaculture city garden between the residences and the AD plant aims to soften the transition and provide attractive views. Also the digester tanks will be sunken and an area will be excavated 4 meters for the tanks to sit in. This means the large steel tanks will not be as overwhelingly visible.
Delivery of animal slurry can be a dirty process. It must be ensured that tankers delivering animal slurry into the city are clean from animal dung on tyres and chassis so not to cause dirty roads. Food waste
27
1 - Permaculture plots and husbandry 2 - Wild produce plots 3 - Apple Orchard 4 - Jetty for canal trade 5 - Anaerobic digester compound 28
Delivery Strategy Delivery of feedstocks to the site will come from the west down Green Park Road. This access route is the most easily passable and offers good connection to roads leaving Bath. Also coming from the west means that delivery does not have to come through the main Bath high street or past the bus station which is the busiest part of Baths road network. The location of the plant the site allows for easy lorry turning due to the large courtyard designed into the masterplan between the 3 buildings. All pedestrian pathways are away from delivery routes and allow for safe access into the site. Also the digestate store is directly adjacent to the main permaculture plot. This allows for direct fertilisation from the plant to the crops. Along with this, the AD plant building will be used for packaging digestate as a compost alternative and distributing locally via the Bath Farmers Market. Due to the number of allotments around Bath, compost should be a desirable product. The AD plant is located on the farthest corner of the site from the mission theatre so should not be a deterent for customers of the theatre. The folk theatre intends to work inline with the mission theatre. As the folk theatre is a potential festival venue for the Bath Folk Festival held annually in August, security of the plant should be considered. All plant should be suitably fenced off from pedestrians.
Bath City Farm Farm locations local to Bath
29
Access Route 30
Hoval CHP and Boiler plant room
31
Conclusion After completing the process of sizing heating plant and consequently the digester, it was found that a substantial amount of waste was needed to fuel the specified plant in a yearly cycle. For the scheme to be viable it will need constant support from its local farms and the support of the city of Bath. During masterplanning of the site it was envisaged that an AD plant would need a substatial amount of space for all the processes that come with it. Overall that side of the brief was suitable. With all the incentives that come with renewable generation,the AD project is a feasible venture and one which limits landfill waste and also gives back to the community when the correct strategy is set up.
32
Reference List
Agrivert (2008) Planning Application for Anaerobic Digestion Facility at West Lodge Farm, Courteenhall Anaerobic Digestion: www.biogas-info.co.uk/index.php/what-is-anaerobic-digestion.html [Accessed February 2014] Bio-Methane to Grid; http://www.cngservices.co.uk/biomethane-to-grid/ [Accessed January 2014] BSRIA Guidance Note 12/97 Oversized Heating Plant. Carbon Reduction Commitment; http://www.cclevy.com/page/112/Carbon-Reduction-Commitment.htm [Accessed December 2013] Climate Change Levy Rates; HMRC (2013) DEFRA & DECC (2010). Anaerobic Digestion Strategy and Action Plan Energy and Emissions Projections; https://www.gov.uk/government/collections/energy-and-emissions-projections [Accessed January 2014] Frost & Gilkinson (2011) Performance Summary of AD Plant at AFBI Hillsborough Goodrich (2005). AgStar Fund: Anaerobic Digestion Systems for Mid Sized Dairy Farms Nijaguna, B. (2002). Biogas technology. 1st ed. New Delhi: New Age International. Parker, D. (2009). Micro-generation. 1st ed. Amsterdam: Elsevier/Architectural Press. Planning Policy Statement 10, Annex E Renewable Heat Incentive; http://www.rhincentive.co.uk/eligible/levels/tiered/ [Accessed January 2014] The Climate Change Act; http://www.theccc.org.uk/tackling-climate-change/the-legal-landscape/global-action-on-climate-change/ [Accessed December 2013]
33
Bibliography
Annex B. Feed in Tariff with Contractors for Difference. Gov.uk Beggs, C (2009). Energy: Management, Supply and Conservation. 2nd Edition. Butterworth Heinemann. Beith, R. (2011). Small and Micro Combined Heat and Power (CHP) systems. Advanced design, performance, materials and applications. Woodhead Publishing Ltd Carbon Trust, (2010). CTG008. Monitoring and Targeting. Carbon Trust. UK Carbon Trust, (2010). Technology Guide. CTV044. Introducing combined heat and power. Carbon Trust UK Carbon Trust, (2012). Technology Overview. CTV010. Renewable energy sources. Carbon Trust UK Carbon Trust, (2011). Micro-CHP Accelerator. CTC788. Carbon Trust UK Carbon Trust, (2008). Good Practice Guide. GPG388. Combined Heat and Power for Buildings. Action Energy Carbon Trust (1998). Good Practice Guide. GPG176. Small scale combined heat and power for buildings. Carbon Trust UK Carbon Trust, (2013). Conversion Factors. CTL153. Carbon Trust UK CIBSE, (2006). Guide A. Environmental Design. 7th Edition. CIBSE London CIBSE, (2012). Guide F. Energy Efficiency in Buildings. CIBSE London CIBSE, (2012). AM12. Applications Manual 12. Combined Heat and Power (CHP) and District Heating. CIBSE London CIBSE, (2013) TM54. Evaluating operational energy performance of buildings at the design stage. CIBSE London CIBSE, (2013). TM52. The Limits of Thermal Comfort. CIBSE London CIBSE, (2008). TM46. Energy Benchmarks. CIBSE London CIBSE, (2006). TM22. Energy Assessment and Reporting Methodology. 2nd Edition. CIBSE London Department for Energy and Climate Change, (DECC), (2013). Updated Energy Emissions Projections. Government UK Department for Energy and Climate Change, (DECC), (2013). CHP Focus. Government UK Griffiths, R (1995). Combined Heat and Power. A Practical Guide to the Evaluation, Development, Implementation and Operation of Cogeneration Schemes. Biddles Ltd
34