TECHNOLOGIES TO ENHANCE THE OPERATION OF EXISTING NATURAL GAS COMPRESSION INFRASTRUCTURE
This project has documented and demonstrated the feasibility of technologies and operational choices for companies who operate the large installed fleet of integral engine compressors in pipeline service. Continued operations of this fleet is required to meet the projected growth of the U.S. gas market. Applying project results will meet the goals of the DOE-NETL Natural Gas Infrastructure program to enhance integrity, extend life, improve efficiency, and increase capacity, while managing NOx emissions. These benefits will translate into lower cost, more reliable gas transmission, and options for increasing deliverability from the existing infrastructure on high demand days. The power cylinders on large bore slow-speed integral engine/compressors do not in general combust equally. Variations in cylinder pressure between power cylinders occur cycle-to-cycle. These variations affect both individual cylinder performance and unit average performance. The magnitude of the variations in power cylinder combustion is dependent on a variety of parameters, including air/fuel ratio. Large variations in cylinder performance and peak firing pressure can lead to detonation and misfires, both of which can be damaging to the unit. Reducing the variation in combustion pressure, and moving the high and low performing cylinders closer to the mean is the goal of engine balancing. The benefit of improving the state of the engine ''balance'' is a small reduction in heat rate and a significant reduction in both crankshaft strain and emissions. A new method invented during the course of this project is combustion pressure ratio (CPR) balancing. This method is more effective than current methods because it naturally accounts for differences in compression pressure, which results from cylinder-to-cylinder differences in the amount of air flowing through the inlet ports and trapped at port closure. It also helps avoid compensation for low compression pressure by the addition of excess fuel to achieve equalizing peak firing pressure, even if some of the compression pressure differences are attributed to differences in cylinder and piston geometry, clearance, and kinematics. The combination of high-pressure fuel injection and turbocharging should produce better mixing of fuel and air in lean mixtures. Test results documented modest improvements in heat rate and efficiency and significant improvements in emissions. The feasibility of a closed-loop control of waste-gate setting, which will maintain an equivalence ratio set point, has been demonstrated. This capability allows more direct tuning to enhance combustion stability, heat rate, or emissions. The project has documented the strong dependence of heat rate on load. The feasibility of directly measuring power and torque using the GMRC Rod Load Monitor (RLM) has been demonstrated. This capability helps to optimize heat rate while avoiding overload. The crankshaft Strain Data Capture Module (SDCM) has shown the sensitivity to changes in operating conditions and how they influence crankshaft bending strain. The results indicate that: balancing reduces the frequency of high-strain excursions, advanced timing directly increases crankshaft dynamic strain, reduced speed directly reduces strain, and high-pressure fuel injection reduces crankshaft strain slightly. The project demonstrated that when the timing is advanced, the heat rate is reduced, and when the timing is retarded, the heat rate is increased. One reason why timing is not advanced as much as it might be is the potential for detonation on hot days. A low-cost knock detector was demonstrated that allowed active control to use timing to allow the heat rate benefit to be realized safely. High flow resistance losses in the pulsation control systems installed on some compressors have been shown to hurt efficiency of both compressor and engine/compressor system. Improved pulsation control systems have the potential to recover almost 10% of available engine power. Integrity enhancements and reduced component failure probability will enhance aggregate deliverability. In addition to improving the efficiency of fuel conversion, all increases in compressor efficiency will reduce the fraction of available engine power that must go to overcome losses and, thereby, will add to deliverability. Project results confirm an earlier survey of a large range of compressor efficiency. If the bottom half of the efficiency range is upgraded with improved technology, such that the resulting performance approaches the best documented efficiency, the aggregate system-wide capacity could be increased by 10% with no new installed compression. An additional phase was added to the original scope of work to investigate the perceived imbalance in airflow between power cylinders in two-stroke integral compressor engines.
- Research Organization:
- Southwest Research Institute, San Antonio, TX (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FC26-02NT41646
- OSTI ID:
- 889462
- Country of Publication:
- United States
- Language:
- English
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