1、OR-05-9-2 Demonstration of a 30-kW Microturbine with Heat Recovery in a 500-Soldier Barracks Michele Friedrich, PE Member ASHRAE David L. Smith Peter R. Armstrong, PhD Stephen E. Rowley, PE ABSTRACT A combined heat and power-conjgured microturbine system was evaluated as an alternative to grid-suppl
2、ied elec- tricpower: While off-grid, the system provides auxiliarypower forgus-$red boilers and aportion of the domestic hot water for a 500-man barracks and kitchen. One-time tests were made of sound levels, stack emissions, and power qualiw. Steady-state generating cupaciq droppedfaster than the r
3、atings as the inlet air temperature approached 15OC, while generating eficiency, based on fuel higher heating value, did not drop as rapidly and was still almost 21 % at 33OC. The microturbine must boost the fuel (natural gas) delivery pressure to 55psg. During the one year of operation, four fuel c
4、ompressors failed und there were repeated failures of the microturbine and heat recovery heat exchanger controls. Energy savings based on the measured perfarmance and CY2003 utility rates were $2670per year: INTRODUCTION Escalating energy costs and concerns about electric system reliability, most no
5、tably in California and the North- east, have heightened interest in small-scale power generation as an alternative to dependence on the power grid. Microur- bines have been marketed in the United States since about 1995 for distributed generation and to provide both electricity and thermal energy (
6、when equipped with a cogeneration pack- age) with good overall system efficiencies. Some of the benefits cited for distributed generation and combined heat and power (CHP) systems include: reduced grid-supplied electrical demand reduced consumption of grid-supplied electrical energy reduced costs fo
7、r both electrical energy and electrical demand reduced environmental emissions increased electrical system reliability The project reported in this paper was funded in support of the US military and governmental mission to demonstrate new energy-saving technologies in federal facilities. In addi- ti
8、on, funds were committed under a federal new-technologies deployment program to measure and veri performance of the CHP microturbine system, The CHP system includes a 30-kW (nominal) recuperated microturbine, capable of both grid-parallel and grid-indepen- dent operation, and an exhaust gas heat rec
9、overy unit compris- ing a heat exchanger, water circulation pump, bypass damper, and controls. The system was installed in a 119,000-square- foot, 500-man army barracks and administration complex with full (three meals per day) dining facilities. The system uses natural gas to produce electricity to
10、 supplant a fraction of the grid-supplied electricity and uses the recovered exhaust gas heat for domestic hot water (DHW). A step-down trans- former reduces the microturbine generator?s 480-volt, three- phase output to 208-volt, three-phase to match the building?s electrical distribution system. Th
11、e microturbine exhaust gas is ducted to the plate/fin-type heat exchanger to preheat domes- tic hot water for the barracks and dining hall. Grid failure will initiate a microturbine shutdown and disconnection from the grid. Restart is delayed for approximately five minutes. Upon restart, the microtu
12、rbine will function in grid-independent mode with the generated electricity serving only dedicated circuits that include lighting within the mechanical room, natural gas-fired boilers, the DHW circulation pump, and a hot-water circulation pump that provides space conditioning for the barracks. Resto
13、ration of grid power will cause the microturbine to shut down and restart in grid-parallel mode. Michele Friedrich, Peter R. Armstrong, and David L. Smith are research engineers at Pacific Northwest National Laboratory, Richland, Wash. Stephen E. Rowley is the energy manager, Public Works Department
14、, Fort Drum, N.Y. 02005 ASHRAE. 791 This paper describes the installed cogeneration equip- ment and its interface with the buildings existing DHW and electrical systems. The instrumentation used for performance verification is also described. Actual performance, based on continuous monitoring and on
15、e-time tests, is analyzed and documented. Performance measured under field conditions is compared to rated performance, operational experience is summarized, and recommendations are made for improved operation and efficiency. MICROTURBINE AND HEAT EXCHANGER SYSTEM The CHP system consists of a low-pr
16、essure 30 kW micro- turbine, a fuel compressor (to boost natural gas pressure from Table 1. Microturbine Specifications at Full Power and IS0 Conditions* Output voltage Electrical frequency Efficiencv at IS0 400-480 VAC 50/60 Hz, 3-phase 26% LHV (23% HHV) Gas side flow rate 1096 kdh Natural gas cons
17、umption Exhaust gas temperature 122 kW HHV 261OC * International standard temperature, 15T, pressure, 1 atmosphere, and humid. ity, 60% RH. NOx production Sound level Weieht 9 ppm 15% O, 58 this is the assumption made by the microturbine manu- facturer in the demonstration model product specificatio
18、ns (MT Manufacturer 2002). A watt transducer was used to measure net power out of the microturbine. The internal power requirements and losses between the turbine and the power terminals, including fuel compressor power, generator losses and power converter losses, are thus included in OUT definitio
19、n of turbine efficiency. The volumetric flow rate and temperature differential of the water in the heat recovery heat exchanger were measured to calculate the heat energy recovered from the microturbine exhaust gas. The specific heat of the water was assumed to be constant over the range of 10C to 7
20、0C (38F to 158F). The inlet and outlet water temperatures and inlet and outlet gas temperatures of the heat recovery heat exchanger (RHX) were also measured to calculate the log-mean temper- ature difference (LMTD), effectiveness, heat exchange modu- lus (number of transfer units, or NTU), and overa
21、ll conductance (UA) of the heat exchanger. The pressure and temperature of the fuel as well as the temperature, humidity, and pressure of the air were measured to assess their affect on the performance of the microturbine. Figure 3 shows the gas metering installation. All of the data collected on th
22、e data acquisition system were sampled at a rate of 0.2 Hz (once every five seconds) and at an aggregating and logging rate of once every five minutes. The sensors are described by function in Table 3. Data Reduction A short program was written to aggregate the data over each hour and load into a sp
23、readsheet where the following calculations were made:2 Rate of heat recovery: RHX heat recovery (kW) = GPM, * (0.0037854 m3/gal) * pw * Cp * dTw (60 slmin) Because the gas meter, water meter, Btu meter, and power meter pulse rates are often less than 0.2 Hz, care was taken to evaluate performance me
24、trics based on time intervals of sufficient duration to collect at least 200 puises. 2. All reported values are based on time intervals with “constant“ flow rates, that is, the one-minute average flow rates were all within *2% of the interval average and the number of pulses per minute vaned by no m
25、ore than *I from the interval average. 1. Figure 3 Natural gasjlter and metering. Log-mean temperature difference at the RhX: RHX LMTD TC) (Tmin - Twou3 - (Tgasout - Twin) 1 In (Tmin - Twout) 1 (Tamui- Twin) Instantaneous thermal conductance of the RHX: RHX UA (kW1“C) = RHX heat recovery I RHX LMTD
26、Heat exchanger effectiveness of the RHX: RHX Effectiveness = (Tga, - TgaSOut) I (T, - Twin) Water-side thermal capacitance rate: C, (kW1“C) = mdot * Cp Exhaust-side thermal capacitance rate: Cmin (kW/“C) = Cm, * (Twotit - Twin) 1 (Tgasin - gasout) Heat exchange modulus: RHX NTU= RHX UA I C, Fuel con
27、sumption rate in terms of higher heating value: Fuel in power (kW) = ACFM, * (Pgas I Pref * Tref I Tgas) * (60 mia) * HHVgas I (3.413 BtunV) Turbine-generator-coverter eficiency based on higher heat- ing value of fuel: Efficiency of microturbine = net electric power out I fuel in power Heat recovery
28、 eficiency based on higher heating value offuel: Efficiency of RHX = RHX heat recovery I fuel in power System eficiency based on higher heating value of fuel: Efficiency of = (electric P + RHX heat recovery) I fuel in power 794 ASH RAE Transactions: Symposia Table 3. Equipment List for Performance M
29、onitoring Sensor Measurement Air temperature at inlet Type Unit Accuracy Type T, special limits “C 0.1“C Air relative humidity Air flow meter (e) Atmospheric pressure Thin-film capacitive %RH 1.5% RH Steel diaphragm, strain gage in. WC 0.005 in. WC Steel diaphragm, strain gage dar 5.5 mBar Fuel flow
30、 meter Fuel delivery temperature Fuel delivery pressure Water flowlBTU meter Water temperature 1 Data acquisition system (UP, 2MB, RS-232, programmable I I I Positive displacement diaphragm ACFM 0.5% of reading Type T, special limits “C 0.1“C Steel diaphragm, strain gage Psig 0.1 psig Matched RTDs &
31、 PD water meter Type T, special limits “C 0.1“C GPh4kBTU 1% of full scale Watt meter RHX gas differential pressure Exhaust temperature I Exhaust gas CO I Combustion analyzer I ppm I 5%ofreading I 3-phase Hall effect with CTs kWe 0.2 kW Steel diaphragm, strain gage in.WC 0.1 in. WC Type T, special li
32、mits “C 0.2“C 1 Exhaust eas O, 1 Combustion analvzer I % I 1% I Power quality Exhaust gas NOx where GPM, Pw CP w dTw Pref gasin Gout gasout Tref Twin mdot i -phase digital handheld insrument Combustion analyzer PPm 1 PPm THD% 1 % of full scale ACFMgas = - Pgas gas HHVgas = - electricP = water volume
33、tic flow rate from the flow meter in gallons per minute water density in kg/m3 water specific heat for inlet conditions in Jkg-K water differential temperature from thermocouples (“C) 101.3 kPa temperature of the exhaust gas into the heat exchanger from thermocouple (“C) temperature of the water out
34、 of the heat exchanger from thermocouple (“C) temperature of the exhaust gas out of the heat exchanger from thermocouple (“C) 273.15 K temperature of the water into the heat exchanger from thermocouple (“C) calculated water mass flow rate in kgh actual volumetric flow of natural gas from the flow me
35、ter in cubic feet per minute absolute pressure of the natural gas (Wa) temperature of the natural gas (K) monthly average higher heating value of the gas given by the utility (Btustandard ft3) electric power out of the microturbine measured by watt meter (kW). Note that system efficiency does not ac
36、count for power used by the RHX water pump because we did not measure the split between power dissipated to ambient (wasted) and power added to the water stream (useful). ONE-TIME TEST PERFORMANCE In May 2002, the turbine was operated manually to obtain performance data at a series of partial load o
37、perating points. In addition to the variables measured by the data acquisition system, several one-time measurements were made to charac- terize emissions, combustion efficiency, and inlet airflow. The results of these tests are reported in this section. Average Input, Output, and Inferred Losses Th
38、e sensor data and associated derived values are reported in Table 4 for six periods of steady-state operation, each of four minutes duration. Eficiency was measured by dividing the output by the lower heating value of the fuel. Heat recovered (RHX) is calculated as shown in the “Data Reduc- tion“ se
39、ction using specific heat of water at 60F.3 Exhaust loss is approximated as QMTerh * (Tgaso, - Tair)/ (Tgasin - Tair) where QMTah is the energy in the exhaust gas leaving the microturbine and is equal to the fuel “V minus electrical output (thermal equivalent). Jacket loss is taken to be 3. There is
40、 little variation in Cp of water from 10C to 70C. Cp = 4180 Jkg-K / 0.4%. ASH RAE Transactions: Symposia 795 Firing Rate (“/O full load) Enerpv Balance kW) 100% 86% 75% 56% 37% 18% HHV fuel input RHX outt3ut 126 110 1 O0 83 64 47 68 61 54 44 36 14 Net electrical output I 21 I 21 I 20 I 18 I 15 I 10
41、I Electrical output Est. jacket loss 27 23 20 15 10 5 23 19 19 20 15 23 Energy Balance (% HHV) Heat recovery 54 55 54 54 56 31 Jacket loss Exhaust loss the balance of fuel HHV and, as such, includes turbine/gener- atorhnverter losses and fuel compressor power as well as mie jacket losses. Emissions
42、were measured using a combustion gas analyzer. Calibration gases were shipped to the site, but no adjustments were needed because the analyzer was found to be in good calibration. Exhaust gas constituents were measured at each of six microturbine firing rates, as summarized in Table 4. A comparison
43、between the manufacturers specifications (MT Manufacturer 2002) and test data for partial-load effi- ciency is shown in Figure 4. The manufacturers data were modified to account for the air pressure and temperature at the test conditions. The microturbine efficiency decreases less than 4 percentage
44、points, from 23.1% to 19.4%, with a 50% reduction in electrical power generation. Airflow Measurement Inlet airflow rate cannot be measured directly without interfering with turbine operation (e.g., increased pressure drop). However, the existing inlet channel can serve as a flow element if properly
45、 calibrated. A one-time calibration was performed using a standard flow hood to obtain the following relation with a standard error = 4.7%: 18 17 19 24 24 49 7 7 7 4 5 10 vf literh = 60.7 Apo. wherep is in pascals, or vf cb = 2035 Apo. where Ap is in inches WC. Combustion Analysis3 o7 (%) Sound Leve
46、l Measurement Sound level measurements were taken by the sites indus- trial health staff when all other boiler room equipment was turned off. The results generally confirm the manufacturers data but are not directly comparable because the boiler room is moderately reverberant. The measured sound lev
47、els are shown in Table 5. 18.2 18.3 i 8.4 18.4 18.6 18.7 Electrical Quality Measurement Power quality measurements were taken at the generator disconnect with the microturbine connected and delivering power. A second set of measurements was taken with the microturbine disconnected. The same recordin
48、g instrument, a high-quality power harmonics analyzer, was used in both instances. Total harmonic distortion (THD) is a commonly used measure of power quality. THD measures the amount of energy present outside the primary power frequency, in this case 60 Hz. For example, 50% THD would indicate that
49、the CO (actual ppm) NOx (actual ppm) Efficiencv % coz (%) 796 10 27 74 93 50 99 i .6 1.6 1.5 1.5 1.4 1.3 1.5 0.5 O O 20 11 19 18 18 17 16 12 ASHRAE Transactions: Symposia Combustibles (“h) O o. 1 0.5 O. I o. 1 O. 1 20.0 - 15.0 - g 10.0 - 5.0 I - Test Daia Efciency -Capstone Efciency deraied for Temperabe and Pressure from EO 1 0.0 J 0.0 5.0 10.0 15.0 20.0 25.0 30.0 PowerOut(kW) Figure 4 Comparison of manufacturers spec$cations of partial-load eflciency PA of HHV) with measured data. Table 5. Sound Level Measurements Dist
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