Process Optimisation of Brewery Plant with Biogas fired CHP/Trigeneration

Transcription

1 Process Optimisation of Brewery Plant with Biogas fired CHP/Trigeneration Dawei Wu a, Barbara Sturm a, Stephan Hugenschmidt b, Anthony P. Roskilly a a Newcastle Institute for Research on Sustainability, Newcastle University, Newcastle upon Tyne, NE1 7RU, United Kingdom b Department of Thermal Process Engineering, University of Applied Sciences Konstanz, Konstanz, Germany 26/10/2011 SusTEM2011 Newcastle 1

2 Brewing industry in the UK Brewing is the third largest sector of the EU food industry after Dairy and Meat Production. In 2009, 46.8 million hl beer is produced in the UK with a market value of 22.4 billion and consumed 9.0 PJ(10 15 J) of energy. Up to summer 2000, four companies accounted for around 84% of beer production in the UK. In the UK, increasing numbers of small/medium size brewery plants are still playing an important role in this industry. The number of breweries in the UK increased from 502 in 2003 to 745 in Specific Energy Consumption (MJ/hl) e th min max e el min max e tot min max Ref[3] Ref[4] Ref[5] /10/2011 SusTEM2011 Newcastle 2

3 Energy distribution in the brewery The typical energy consumption distribution is divided into two sections: thermal energy and electricity. The brewhouse, including mashing and wort boiling processes, consumes about 50% thermal energy needed. The cooling division with 30% of the total demand of electricity is the major consumer followed by the bottle filling process. Thermal Energy Brewhouse 30-60% Packaging 20-30% Space heating <10% Utilities 15-20% Electrical Energy Refrigeration 30-40% Packaging 15-35% Compressed air 10% Brewhouse 5-10% Boiler house 5% Lighting 6% Other 10-30% 26/10/2011 SusTEM2011 Newcastle 3

4 Brewing process 26/10/2011 SusTEM2011 Newcastle 4

5 Energy balance of one batch in the process Energy form Temperature range ( C) Process Quantity (MJ) Time period Heating 4-70 Mash Tun min Heating 4-73 Mash Tun min Heating Wort Copper min Cooling Heat Exchanger min Cooling 20-9 Fermentation Vessel days Cooling 9-1 Heat Exchanger min Cooling 1 Conditioning Tank days 26/10/2011 SusTEM2011 Newcastle 5

6 Organic wastes in breweries and their applications Brewer s spent grain (BSG) is the major waste of the brewing sector, which represents around 85% of the total by-product generated. Spent grain accounts for about 31% of the original malt weight which is approximately 20 kg per hectolitre beer produced. BSG is often sold as livestock feed with an average profit close to 5 /ton, because of its high content of protein and fibre. Other wastes generated in the brewing process are trub, yeast surplus, kieselguhr sludge and various waste waters. Using brewery wastes by anaerobic digestion to generate biogas (mainly methane) has been explored since the middle of the last century. The methane productivity is liter/g dry substrate. 26/10/2011 SusTEM2011 Newcastle 6

7 Organic waste generation in one batch Main mass flows Wort Process Mass (kg) Solids mass percentage (%) Organic wastes Mass (kg) Solids mass percentage (%) Utilisation for AD Mash Tun Spent grains Yes Wort Copper Wort loss Yes Whirlpool Wort loss Yes Trub Yes Fermentation Beer loss Yes Centrifugation Beer loss Yes Impurities Yes Beer Conditioning Beer loss Yes Filtration Impurities in kieselguhr unknown No Packaging Beer loss No 26/10/2011 SusTEM2011 Newcastle 7

8 Biogas production from anaerobic digestion The overall organic waste that could be applied to anaerobic digestion is kg/ per batch, in which the solids content is kg. The methane production from the organic wastes in one batch is about l. The total chemical energy contained in the methane can be calculated and about MJ thermal energy can be released from the biogas. A two-stage sequential digestion system is preferred, which consists of two reactors: both can operate at mesophilic (35 C) or thermophilic (55 C) mode. 26/10/2011 SusTEM2011 Newcastle 8

9 Brewing process energy consumption in the example plant Day New batch No No. of fermentation vessels(fv) in use No. of batches transfer from FV to CT No. of 5th day fermentation vessels No. of conditioning tanks(ct) in use Heating demands in brewhouse (MJ) Average thermal power demands (kw) Transfer cooling demands (MJ) th day FV cooling demands (MJ) Conditioning cooling demands (MJ) Continuous base load cooling (kw) Surge cooling (kw) Electricity for base load cooling (kw) Peak electricity for total cooling (kw) The brewery operates 24 batches in 7 days, 4 new batches per day for the first 5 days and 2 new batches per day for the last 2 days. There are 26 dual purpose vessels in the brewery, which are operating as either fermentation vessels or conditioning tanks. To maximize the productivity, except for 2 spare vessels, the other 24 vessels are always full. 26/10/2011 SusTEM2011 Newcastle 9

10 Biogas fired CHP selection A CAT G3406 NA Gas Package Generator Set for Biogas with continuous 103 kwe / 129 kva output. The biogas consumption on 100% load is 57.6 Nm3/hr based on the biogas calorific value of kj/m3. The heat contained in this amount of biogas is 350 kwth. Recoverable heat rejection from jacket water: 123 kw; from the exhaust: 84 kw. Electricity generation efficiency: 29.5%. The external burner for Wort Copper is reserved and uses the surplus biogas. In a 15 day cycle time, the biogas fuel energy generated is up to MJ, the total biogas fuel energy needed for electrical cooling is MJ and leave MJ surplus fuel energy which could be used for thermal demands. 26/10/2011 SusTEM2011 Newcastle 10

11 Integration of biogas fired CHP/Trigeneration 26/10/2011 SusTEM2011 Newcastle 11

12 Scenario comparison Scenario 1: AD system + Biogas CHP/Trigeneration + Biogas burner Scenario 2: AD system + Biogas boiler/burner + Electrical chillers Scenario 3: AD system + Biogas boiler/burner + Biogas fired absorption chillers Utility energy saving (kwh) Utility bill saving ( ) Total bill saving ( ) CHP/Trigenneration + Biogas burner Electricity Heat Biogas boiler Heat Absorption chiller + Biogas boiler Electricity Heat /10/2011 SusTEM2011 Newcastle 12

13 Conclusion Simply to sell the wastes as livestock feed isn t the best sustainable solution for the brewer, when compared with biogas production through anaerobic digestion of these wastes. Biogas could provide enough energy for the brewing house, the fermentation and the conditioning stages in a medium size brewery m 3 methane produced in a 15 day cycle time. A 103 kw e biogas CHP/Trigeneration system plus a burner and electrical chillers provides the brewhouse of MJ heating and supplies electricity to drive chillers fulfilling the base load cooling and the surge peak cooling demand of kw as well. In a scenario comparison from an angle of utility savings, the CHP/Trigeneration plus boiler solution shows a utility bill saving of , which exceeds the savings of the biogas boiler alone scenario and the absorption chiller scenario. 26/10/2011 SusTEM2011 Newcastle 13

14 Thank you for your attention! 26/10/2011 SusTEM2011 Newcastle 14