Project Title: Integrated Gas Turbine Gasifier Pilot-Scale Power Plant Contract Number: RD3-71 Milestone Number: 7 Report Date: June 23, 2011

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1 Energy & Environmental Research Center University of North Dakota 15 North 23rd Street, Stop 9018 Grand Forks, ND Project Title: Integrated Gas Turbine Gasifier Pilot-Scale Power Plant Contract Number: RD3-71 Milestone Number: 7 Report Date: June 23, 2011 Principal Investigator: Phillip Hutton Contract Contact: Corey Irion Phone: (701) Phone: (701) Congressional District (Corporate office): Not Applicable Congressional District (Project location): Not Applicable MILESTONE REPORT Executive Summary: During this milestone period, the Energy & Environmental Research Center (EERC) completed Milestone 7 and 8; start of modified microturbine shakedown testing and commenced system construction. The modifications to the microturbine combustor were completed and shakedown testing commenced. Work is ongoing on Milestones Project funding was provided by customers of Xcel Energy through a grant from the Renewable Development Fund. Technical Progress: This quarter the EERC worked concurrently on Milestones 7 and 8. Modification of the gasifier to address the clinker issue was completed and testing recommenced on coal and biomass. Conversion of the C30 Capstone microturbine to an indirectly heated microturbine was completed and shakedown testing of the turbine commenced, as per Milestone 7. Figure 1 shows a simplified system design for a conventional gas turbine based power system. Compressed air is preheated by a recuperator and then injected into a combustor. The hot, pressurized gas exiting the combustor turns the expansion turbine which, in turn, operates the compressor and electric generator. Syngas from a gasifier must be cleaned of particulates and acid gases, and compressed to high pressure to inject into the combustor. The compressor cannot handle hot input gases, requiring cooling of the syngas before compression. This, in turn, requires extensive syngas scrubbing systems between the gasifier and compressor. The capital and operating costs of the syngas scrubbing system in this type of design may exceed that of the gasifier and gas turbine, making this system uneconomical for distributed power production. 1

2 Gasifier Compressor Exhaust Syngas Air High Pressure Microturbine Figure 1. Directly heated gas turbine system for biomass power production To overcome these issues, the system was designed to employ an indirectly heated gas turbine, as presented in Figure 2. Hot syngas is fed to an atmospheric combustor which then heats high temperature air through a high temperature heat exchanger. The high temperature heat exchanger is designed to reduce gas temperatures to an acceptable level for the stock recuperator. Since the syngas never contacts the high speed turbine, particulate cleanup requirements are greatly reduced. The compressor is eliminated, and the need to cool the syngas below the condensation temperature of tars is also eliminated. This eliminates tar fouling in the pipes and greatly reduces the particulate cleanup requirements. The EERC has modified an off-the-shelf Capstone C30 microturbine to move the combustor out of the high pressure zone and into the low pressure zone. A new combustor and heat exchanger was installed in the microturbine to work with the stock recuperator.

3 Exhaust Gasifier Air High Pressure Microturbine Figure 2. Indirectly heated gas turbine system for biomass power production The microturbine modifications were completed in November and testing commenced in December. Figure 3 shows an image of the original modified microturbine. Both the high temperature heat exchanger and combustor are integrated into a single unit and installed directly to the recuperator to minimize pressure losses. A total of 127 individual tests were conducted over a 10 week period. Multiple tests were often conducted on the same day. Testing of the microturbine requires one operator and one engineer. Testing was performed to: Determining operating procedures to overcome the stock software start-up faults Determine the placement of the turbine igniters Determine fuel flow rates to the various injection ports Determine the TET thermocouple location for safe operation, while overcoming preprogrammed start-up and shutdown faults Troubleshoot and shield the source of electromagnetic noise Determine air flow characteristics in the combustor Determine fuel flow characteristics in the combustor for different injection ports Determine operating conditions necessary to maintain a stable flame Initial testing demonstrated erratic and non-reproducible software faults from the stock programming. The cause was eventually found to be excessive electromagnetic interference from the cables feeding the igniters. During initial testing, one of the circuit boards in the C30 stopped working. The igniter cables were shielded and the circuit board replaced. Subsequent software faults were reproducible, indicating that the electromagnetic interference issue was resolved. The two primary software faults were related to the turbine exit temperature (TET) thermocouple location. A start-up fault occurs 30 seconds after ignition if the TET thermocouple does not see a 50 o F rise in temperature. An over-temperature fault occurs if the TET temperature exceeds 1,317 o F. Placement of the thermocouple near the stock recuperator (furthest from the flame front) results in a start-up fault. Placement of the thermocouple closer to the flame front overcomes the start-up fault, but results in an over temperature fault shortly after the turbine

4 shifts into run mode. Subsequent testing was able to overcome the initial start-up faults by locating the TET thermocouple at the end of the combustor. However, an over temperature fault occurred shortly thereafter, indicating that heat transfer between the flame front and thermocouple was insufficient to allow the turbine temperature to reach a steady state operating condition. The turbine combustor was redesigned to increase heat transfer between the flame front and thermocouple by increasing the surface area between the two tenfold. In addition, visual observation of flame stability and location were used to optimize igniter location and fuel injection ports. Ramping of the turbine from 45,000 rpm to 90,000 rpm shifted the flame front and blew out the flame. The turbine combustor fuel injection ports were redesigned to allow premixing of fuel and air within the injection ports to maintain the flame front at a single location throughout the turbine operating speed. Table 1 provides a sample of the parameters recorded and analyzed during testing. The parameters recorded included, but was not limited to, timing, engine speed, generator power, turbine exit temperature, valve positions, inlet fuel pressure, and stock programming commands. Figure 3 provides an example of the turbine speed and turbine exit temperature during one of the tests. The following conclusions and accomplishments were reached following the initial round of testing on the modified turbine: 1. Ignition and light-off of the turbine was accomplished with the current design and stock software. 2. The air flow and gas flow patterns at the output of the expander and input to the combustor were identified. This allows the heat exchanger fins to be designed to provide minimum backpressure and maximum heat transfer. 3. The location of the TET thermocouple is critical to allow both start-up and prevent the over-temperature shutdown fault. 4. The heat transfer from the combustor to the high pressure air must be increased to reduce the temperature at the TET below 1,317 o F at steady state operation. 5. The flammability limits of natural gas occur between 5% and 15% natural gas. The high air flow through the turbine limits the combustion zone to a narrow 5 inch zone along the length of the combustor. The position of the combustion zone varies with air flow, requiring either multiple igniters along the length of the combustor, or independent burner nozzles to maintain ignition temperatures within the combustion zones. The following additional modifications were made to the turbine to overcome the limitations encountered during the first round of testing: 1. Independent burner nozzles were added to provide independent air and fuel premixing within the combustor. 2. The size of the heat exchanger was increased by an order of magnitude to provide increased heat transfer. This was made possible by observations of the air flow patterns at the output of the expander. 3. The input to the high pressure vessel of the turbine was thermally isolated from the output. This will increase peak temperature at the expander inlet and overall heat transfer of the heat exchanger.

5 Figures 4a and 4b show the progression of the turbine from the first iteration to the current version. Initial light-off of the current version is expected to occur Monday, May 23, Additional Milestones/Project Status: Work has commenced on Milestone An update status and expected completion dates for Milestones 9 12 are provided as follows: Milestone 9 Complete Power System Construction: The gasifier, feed system and cyclones have been connected and fully tested on wood, coal and corn. Completion status is 85% complete. The final step is connection of the new microturbine and safety valves. Projected completion date is June 30, Milestone 10 Commence testing and demonstration: There is currently over 1500 lbs each of corn stover, switch grass, wood and corn on the EERC premises. Procurement of biomass is % complete, depending on how many different types of biomass we can run in a reasonable timeframe. Commencement of testing and demonstration is expected to occur a minimum of one week to a maximum of two weeks after completion of the power system. Projected completion date is July 15, Milestone 11 Complete testing and demonstration and document performance data of the power system: Performance data is currently completed for the gasifier and feed system. Performance data for the complete system is pending completion of Milestone 9. Based on the performance data for the gasifier and feed system, completion status is estimated to be 33%. The projected completion date for this Milestone is August 31, Milestone 12 Complete final report detailing the results and findings of the project: The final report is partially completed for all work up to March 1, It is currently at 46 pages and is expected to be near 80 pages upon incorporation of the microturbine and demonstration results. Based upon page count, the completion status is 50%. The projected completion of the final report is September 30, Table 2 provides a summary of the contractual dates and the expected completion dates of Milestones Additional AVI files and images are available upon request.

6 Table 1 Sample of microturbine test data Control Date Control Time Engine Speed (rpm) Main Gen Power TET#1 ( F) TET#2 ( F) Turbine Exit Temp Compress or In Valve Position Feedback % Power Demand (W) Start Command (0/1) Fuel Valve Command Fuel Inlet P HP (psig) Fuel Valve Inj State 2/7/2011 9:13: /7/2011 9:13: (4) - 5, /7/2011 9:15: /7/2011 9:15: (170) 25,000-2/7/2011 9:15:02 0 (1,136) (1,165) 25,000 (1,134) 2/7/2011 9:15:03 20,608 (2,703) (3,093) 25,000 (2,703) 2/7/2011 9:15:04 25,042 (1,718) (2,263) 25,000 (1,717) 2/7/2011 9:15:05 25,064 (823) (1,467) 25,000 (821) 2/7/2011 9:15:06 25,050 (587) (1,143) 25,000 (585) 2/7/2011 9:15:07 25,070 (573) (1,121) 25,000 (571) 2/7/2011 9:15:08 25,044 (567) (1,121) 25,000 (566) 2/7/2011 9:15:09 25,052 (566) (1,126) 25,000 (566) 2/7/2011 9:15:10 25,066 (571) (1,121) 25,000 (569) 2/7/2011 9:15:11 25,086 (570) (1,121) 25,000 (569) 2/7/2011 9:15:12 25,064 (571) (1,121) 25,000 (569) 2/7/2011 9:15:13 25,056 (569) (1,121) 25,000 (569) 2/7/2011 9:15:14 25,064 (566) (1,148) 25,000 (569) 2/7/2011 9:15:15 25,078 (567) (1,148) 25,000 (566) 2/7/2011 9:15:16 25,082 (572) (1,148) 25,000 (566) 2/7/2011 9:15:17 25,090 (577) (1,165) 25,000 (571) 2/7/2011 9:15:18 25,066 (570) (1,176) 25,000 (577) 2/7/2011 9:15:19 25,084 (574) (1,170) 25,000 (569) 2/7/2011 9:15:20 25,070 (570) (1,159) 25,000 (571) 2/7/2011 9:15:21 25,082 (574) (1,159) 25,000 (569) 2/7/2011 9:15:22 25,076 (568) (1,159) 25,000 (571) 2/7/2011 9:15:23 25,064 (562) (1,170) 25,000 (566) 2/7/2011 9:15:24 25,086 (570) (1,165) 25,000 (560) 2/7/2011 9:15:25 25,056 (569) (1,165) 25,000 (569) 2/7/2011 9:15:26 25,082 (568) (1,165) 25,000 (569) 2/7/2011 9:15:27 25,076 (566) (1,165) 25,000 (566) 2/7/2011 9:15:28 25,072 (571) (1,165) 25,000 (566) 2/7/2011 9:15:29 25,086 (571) (1,154) 25,000 (569) 2/7/2011 9:15:30 25,072 (570) (1,165) 25,000 (569) 2/7/2011 9:15:31 25,092 (571) (1,165) 25,000 (569) 2/7/2011 9:15:32 25,050 (555) (1,165) 25,000 (569) 2/7/2011 9:15:33 25,086 (574) (1,176) 25,000 (555) 2/7/2011 9:15:34 25,092 (552) (1,176) 25,000 (571) 2/7/2011 9:15:35 25,056 (562) (1,148) 25,000 (549) Output Power (W) Gen Speed Cmnd Gen Power Out (W)

7 Table 2 Contractual and expected completion dates of Milestones Milestone Contractual Due Date Expected Completion Date 9 April 1, 2011 June 30, July 1, 2011 July 15, October 1, 2011 August 31, January 1, 2012 September 30, ,000 1,400 80,000 70,000 60,000 Engine Speed (rpm) Turbine Exit Temp ( F) 1,200 1,000 RPM 50,000 40, Temperture F 30,000 20, , Seconds Figure 3 Example of the turbine speed and turbine exit temperature during one of the microturbine tests. -

8 Figure 4a initial version of indirectly heated microturbine

9 Figure 4b Current version of indirectly heated microturbine LEGAL NOTICE THIS REPORT WAS PREPARED AS A RESULT OF WORK SPONSORED BY XCEL ENERGY. IT DOES NOT NECESSARILY REPRESENT THE VIEWS OF XCEL ENERGY, ITS EMPLOYEES, OR THE RENEWABLE DEVELOPMENT FUND BOARD. XCEL ENERGY, ITS EMPLOYEES, CONTRACTORS, AND SUBCONTRACTORS MAKE NO WARRANTY, EXPRESS OR IMPLIED, AND ASSUME NO LEGAL LIABILITY FOR THE INFORMATION IN THIS REPORT; NOR DOES ANY PARTY REPRESENT THAT THE USE OF THIS INFORMATION WILL NOT INFRINGE UPON PRIVATELY OWNED RIGHTS. THIS REPORT HAS NOT BEEN APPROVED OR DISAPPROVED BY XCEL ENERGY NOR HAS XCEL ENERGY PASSED UPON THE ACCURACY OR ADEQUACY OF THE INFORMATION IN THIS REPORT.