Digester Gas Utilization and Cogeneration. Tom Mossinger, P.E.

Transcription

1 Digester Gas Utilization and Cogeneration Tom Mossinger, P.E.

2 Presentation Outline 1. Energy Management What is the big deal? 2. Cogeneration at WWTP s a. Technology and related operational issues b. Recovering and utilizing heat c. Maintenance and digester gas cleanup d. Operating in parallel with utility e. Other tips tm707weau.ppt/2

3 October 2007 August 2007 tm707weau.ppt/3

4 U.S. Department of Energy - Energy Efficiency and Renewable Energy Federal Energy Management Program, Director Beth Shearer Typical headlines that we have been seeing in the news lately are: "Hurricane Isabel Batters the East Coast; Federal Government Shut Down" "Massive Blackout Shuts Down New York City" "Natural Gas Prices Expected to Remain High" "Bills to Rise as Mercury Drops" tm707weau.ppt/4 "Electrical Grid Vulnerable to Hackers, Viruses"

5 tm707weau.ppt/5 NEARLY a century ago, Henry Ford declared a customer could have a car in any color as long as it was black. Now, carmakers around the world are trying to convince consumers that their lineups come in green. From BMW to Honda, from Chrysler to Volkswagen, the industry is rushing to make vehicles that use less gasoline or don t rely on it at all.

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7 Sustainable Planet Green Way of Living Renewable Energy tm707weau.ppt/7

8 From Conservation to Population, a New Look at Planet Earth New Options Needed tm707weau.ppt/8

9 Need for Energy Management in Water and Wastewater Industry 1. Water & wastewater services account for 30-50% of municipal energy use 2. Equivalent to 3-4% of nations energy use to 30% of the cost for wastewater systems operations is for power to 35% of the cost for water systems operations is for power Municipal Agencies being asked to do more with less. tm707weau.ppt/9

10 Cogeneration at Wastewater Treatment Plants

11 Cogeneration Technologies 1. Reciprocating Engines (>250 kw) 2. Micro Turbines (30 to 250 kw) 3. Gas Turbines (>3,000 kw) 4. Fuel Cells (200 to 3,000 kw) 5. Stirling Engines (new technology, 55 kw to 250 kw) tm707weau.ppt/11

12 Reciprocating Engines tm707weau.ppt/12 1. Proven technology for using digester gas 2. Strict air permit regulations 3. Manufacturer s can meet current regulations 4. Regulations moving towards oxidation catalysts which requires good fuel conditioning to remove contaminants

13 Reciprocating Engines (continued) 1. Siloxane is an issue, increases O&M significantly 2. Requires <1 psi fuel pressure with low pressure fuel system 3. Higher maintenance tm707weau.ppt/13

14 Micro Turbines 1. Easy to permit (low emissions) 2. Only two manufacturer s with DG experience (limited) 3. Lower efficiency than engines 4. Requires >50 psi fuel pressure tm707weau.ppt/14

15 Gas Turbines 1. Strict air permit regulations 2. Limited manufacturer s with experience on DG 3. Siloxanes and H 2 S are issues 4. Competitive only for larger installations 5. Requires >200 psi fuel pressure tm707weau.ppt/15

16 Fuel Cells tm707weau.ppt/16 1. Experience on DG Santa Barbara, CA LA County Sanitation District, CA Portland, OR Renton, WA Yonkers, NY LADWP, CA Inland Empire Utilities District, CA Tulare, CA Currently being installed at several other WWTP s in CA and elsewhere

17 Fuel Cells (continued) 1. Requires fuel conditioning to remove all contaminants 2. Higher capital cost and maintenance cost 3. High efficiency (>47%) 4. Higher grant money currently available 5. Exempt from air permit requirements 6. Qualifies for simplified interconnection 7. Reduction of greenhouse gases tm707weau.ppt/17

18 Stirling Engines 1. Potential New technology 2. Very promising on DG since external combustion 3. Very tolerant to contaminants 4. Low emissions 5. Requires <1 psi fuel pressure 6. Currently no longer in commercial production tm707weau.ppt/18

19 General Design Considerations tm707weau.ppt/19 1. Fuel availability and type(s) 2. Heating valve 3. Electrical load to be supported 4. Digester gas produced in a WWTP can normally generate enough power to meet 40% to 70% of WWTP s average power requirement 5. The recovered heat from cogeneration equipment is normally adequate to meet heat required by sludge digesters

20 Mechanical Design Considerations tm707weau.ppt/20 1. Fuel system a. Quantity and quality b. Gas filtering and condensate removal c. Gas compressors or blowers d. Gas storage to dampen variations 2. Engine cooling and heat recovery a. Must cool equipment when heat is not needed b. Engines have available jacket water, exhaust and lube oil heat recovery c. Bypass exhaust heat when not needed

21 Mechanical Design Considerations (continued) 1. Lube oil system a. Filtering b. Automatic oil makeup c. Oil analysis 2. Exhaust system a. Sound attenuation b. Back pressure 3. Starting system a. Battery start b. Air start tm707weau.ppt/21

22 Digester Gas Quality and Impact on Maintenance % CO % CH 4 3. Water vapor (saturated) 4. Trace levels of contaminents including H 2 S and siloxanes, grease, dirt, etc. 5. Typically generated at 8-12 inches w.c. tm707weau.ppt/22

23 Contaminants of Concern 1. H 2 S 2. Siloxane 3. Water tm707weau.ppt/23

24 H 2 S 1. Typically present at levels of >2000 ppmv if untreated in the process 2. Forms with water vapor (both in the gas and in the combustion products) to form H 2 SO 4 3. Most air districts regulate H 2 S in some way, typically gas must have levels <200 ppmv tm707weau.ppt/24

25 H 2 S Treatment Options 1. Adsorption (iron sponge) 2. Ferric or Ferrous Chloride into process 3. Water stripping tm707weau.ppt/25

26 Adsorption (Iron Sponge) 1. Potentially combustible 2. Requires high degree of O&M (regeneration/replacement) tm707weau.ppt/26

27 Ferric or Ferrous Chloride Addition 1. Chemical storage/handling/delivery very corrosive 2. Process issues tm707weau.ppt/27

28 Water Stripping 1. Requires consumptive water use at 150 psi 2. Chemical use to clean packing tm707weau.ppt/28

29 Siloxane 1. Several Silicon compounds 2. Derived from several common household products (shampoos, etc.) and dry cleaning solutions 3. Water soluble 4. Causes hard abrasive glass like buildup on combustion equipment such as engine valves tm707weau.ppt/29

30 Siloxane Treatment Options 1. Adsorption (patented products) 2. Remove water from gas (refrigerative drying) 3. Often both are required due to quantity in gas and removal requirements tm707weau.ppt/30

31 Siloxane Removal O&M Issues 1. High O&M (approximately $0.005/kWhr) a. Media replacement b. Energy costs for drying and to overcome pressure losses c. Periodic testing tm707weau.ppt/31

32 Recovering and Utilizing Heat 1. Jacket, exhaust and lube oil heat recovery a. Must cool lube oil and jacket water b. Exhaust heat recover only if needed 2. Utilizing recovered heat a. Heat digesters b. Building heating and cooling c. Sludge drying d. Organic rankine cycle for additional power tm707weau.ppt/32

33 Recovering and Utilizing Heat (continued) 1. Type of heat exchangers to minimize plugging/fouling 2. Chemical treatment of hot water to minimize corrosion 3. Air removal and pressure control within hot water system to minimize corrosion tm707weau.ppt/33

34 Engine Cooling and Heat Recovery System Lube Oil From Engine Lube Oil to Engine J.W. From Engine J.W. To Engine Exhaust From Engine Bypass Valve Lube Oil H.E. Jacket Water H.E. Exhaust HRU Waste H.E. Primary H.E. tm707weau.ppt/34 Recirculation Pump No.3 Water Cold Water From Digesters Hot Water to Digesters

35 Electrical Design Considerations 1. Utility requirements for parallel operation 2. Generator capacity vs. load 3. Standby operation 4. Load shedding 5. Point of connection to system 6. Voltage selection tm707weau.ppt/35

36 Operating in Parallel with Utility 1. Operate in parallel to increase utilization 2. Import/export agreement with utility for ease of operation vs. reverse power relay 3. Standby power during utility outages to improve reliability 4. Regular preventative maintenance tm707weau.ppt/36

37 Simplified Electrical Example tm707weau.ppt/37

38 Standby Operation 1. Is this capacity to be a standby source? 2. Identify and calculate essential load 3. Compare to standby capacity 4. Will load shedding be necessary? tm707weau.ppt/38

39 Load Shedding 1. Does the load exceed generating capacity? 2. Can plant tolerate a short-term outage for restarting? 3. Automatic load shedding required if no outage permissible 4. Circuits must be arranged to supply essential load with other load shutdown tm707weau.ppt/39

40 Procurement 1. Conventional design/bid/build 2. Pre-purchase equipment 3. Design/build (DB) 4. Design/build/operate (DBO) 5. Design/build/operate/own/transfer (DBOOT) 6. And others tm707weau.ppt/40

41 Other Tips for Improved Operation 1. Regular periodic oil testing 2. Avoid oversizing Cogen 3. Check and maintain water chemistry 4. Drain water from DG system 5. Periodically check heat balance 6. Preventative maintenance schedule 7. Adequate staff training tm707weau.ppt/41

42 Summary 1. Design facility considering operation and maintenance issues 2. Wastewater treatment plants are perfect fits for CHP 3. Digester gas fuel needs special attention 4. Need proper design for engine cooling/heat recovery system tm707weau.ppt/42

43 Summary (continued) 1. Pay attention to electrical and controls 2. Preventative maintenance is a key element 3. Avoid over sizing facility 4. Good money making projects 5. Current grant money improves cost effectiveness tm707weau.ppt/43

44 Questions? tm707weau.ppt/44