21-0512 Biofuel Use for SEE Institute

Question

Absorption Chiller

Diamond Developers is building SEE Institute in the award-winning community, The Sustainable City (TSC), Dubai. The project comprises a 5,000 sqm smart building (G+1) offering a central atrium, a VIP room, 2 lecture halls, a multi-purpose hall, and a 500-people amphitheater. The building is designed as a zero-carbon facility for advancing knowledge in sustainability through training, research, incubation, and events. Construction materials and method are carefully selected to reduce the building’s embodied carbon. During operation, all energy consumption will be from onsite renewables, and surplus electricity will be exported (to offset embodied carbon). TSC produces a significant amount of organic waste such as food residues, animal manure, and green waste. Currently, most of that waste is collected and transferred to a local waste management company (some food waste is discharged using the garbage disposal unit under the kitchen sink). An alternative system could divert the waste (called feedstock) to run a small-scale biogas plant in TSC using anaerobic digestion. DD is currently examining one such solution by the Dutch company The Waste Transformers (1). The biogas plant is designed to handle up to 3,000 kg of organic waste per day to produce biogas and a digestate) 2)There is no combustion – digestion will produce app. 320 m3/day of biogas which will be serving a direct-fired absorption chiller through a well-insulated and concealed pipe. The absorption chiller will contribute around 31% of the cooling load required in the SEE Institute which leads to a lower electrical use intensity. Moreover, the digestate will be utilized as a soil conditioner / fertilizer in community landscaping.

Conclusion: Although the absorption chiller is still under review by our design team, Diamond Developers kindly seeks ILFI preapproval of this technology for further consideration. 

With reference to the email dated 31-Dec-2020, Diamond Developers is providing clarifications on the following points: Advantageous Biofuel Sourcing • Local Waste Products: Organic waste such as food residues, animal manure, and green waste. • Beneficial Combustion: There is no combustion – digestion will produce app. 320 m3/day of biogas which will be serving a direct-fired absorption chiller through a well-insulated and concealed pipe. The absorption chiller will contribute around 31% of the cooling load required in the SEE Institute which leads to a lower electrical use intensity. Moreover, the digestate will be utilized as a soil conditioner / fertilizer in community landscaping • Net Zero Annual Emissions: The biogas plant consumes methane preventing it from releasing into the atmosphere. The energy produced is far more than the energy required to run the plant therefore it’s self-sufficient. Biofuel and Combustion Impacts • Displacement of beneficial land use: Not applicable in our case • Depletion of advantageous biomass: Not applicable in our case • Negative externalities: A sister company called “Tadweer” that is based locally and collects the waste from The Sustainable City will be supplying any shortage in waste needed for the Anaerobic Digestor • Short Term Impact: Not Applicable in our case • Fossil fuel replacement: For this project, we plan to design chiller which specially designed to run on Biogas • Air quality impacts: Flue Gas or Air quality is subject to the composition of the Biogas feed entering the Absorption Chiller. Impure Biogas will generate dangerous flue gases. Please note that it is not possible/difficult to monitor Biogas composition leaving Biogas digester. 

Biogas composition confirmed: 

CH4: 60% 
CO2: 40%
H2S: Null
NH3: Null
H2O: Null 

With reference to the email dated 02-March-2021, Diamond Developers is providing clarifications on the following points:
Advantageous Biofuel Sourcing
Q. In the "Beneficial Combustion" section it's stated that "There is no combustion." We wanted to be clear that the captured biofuel is being combusted on site to fuel the direct fire blast chiller. Can you share schematics of the system so we can understand the process in greater detail?
A. We have requested the schematics drawings from the manufacturer which might take time. Meanwhile, please note that we are pursuing consideration of several vendors.
Q. Similarly, we would like to confirm that this infrastructure cannot be switched over to natural gas in the future. Can you confirm that this system is closed-loop and cannot tie into any future natural gas lines that may exist?
A. The absorption chiller can only operate using biogas (60% CH4) which does not allow to connect the system to the natural gas as it consists of 95% CH4. Therefore, there will be no connection of natural gas lines to the absorption chiller.
Biofuel and Combustion Impacts
Q. For the "Air Quality Impacts" section, it's stated that "impure biogas will generate dangerous flue gases." Does this mean then that the biogas you are burning is pure (as you provided those percentage breakdowns)? Is there any chance the biogas would ever have impurities in the future? And if so, how would they be filtered or captured such that there were no negative air quality impacts?
A. There is a two-stage filtration process. The plant will filter such elements as H2S, NH3 and water vapor which have no energy contribution in biogas. Removing these impurities is essential to maintain an appropriate energy density which will be done before the inlet of the absorption chiller.
Q. Lastly, a more optional question, refrigerants are out of scope for our ZC program now, but we were wondering how you are looking at the impacts of these within your chiller system as refrigerants as you surely know can have extremely high environmental impacts.
A. One of the main advantages of absorption chillers is that the refrigerants used in them do not contribute neither to global warming nor to ozone depletion. The chiller will operate using a combination of lithium bromide (LiBr) in a liquid form and water (can be turned into a water vapor). In this case lithium bromide is the absorbent and water is the refrigerant. 
Answer
The project team has shown that their biogas-powered absorption chiller meets all of the criteria within the Biofuel Guidance, and can therefore use this as part of their cooling load energy solution. 
The biogas system does include the combustion of methane gas, which in this case is considered beneficial combustion as the gas is captured from the anaerobic digestion of organic waste produced within the project's boundary. The team detailed the two-step filtration process applied to ensure the methane gas that is burned is pure, minimizing the impact on the local air quality while maintaining an efficient system. The team also addressed that the infrastructure has no potential of being switched to natural gas as the system is designed to only operate off of biogas, and therefore there will never be a connection to a natural gas line.

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