Fig. 7 Effectiveness of Gas-Extraction Valve in Restraining The Hunting
It can, therefore, be said from the above that the basic concept that controlling the flow of exhaust-gas energy into the turbocharger can restrain the hunting in the scavenging and exhaust circuits for stabilized plant dynamic characteristics proved correct, and also that the use of the gas-extraction valve was clearly shown to be effective as a means to implement that concept.
2-6. Improvement of Working Plant Dynamic Characteristics
The confirmation by numerical simulation of the effectiveness of the use of the gas-extraction valve in restraining the hunting as in the preceding chapter was followed by experimental use of the gas-extraction method in the working diesel generating plant to verify its hunting-restraining capability, before finalizing the plant configuration capable of successful power generating operation with low NOx emissions.
The gas-extraction valve employed was a pneumatically operated cage valve as shown in the specification of table 3, which was installed on the exhaust-gas duct between the SCR system outlet and turbocharger gas inlet.
In the working plant, the engine output is varied in response to changing power demands making it necessary for the gas-extraction valve to operate properly in accordance with varying situations. The control system, therefore, was planned in such a manner that in the event of change in engine output, the gas-extraction valve would be activated to control the amount of work to be done by the turbocharger so that the engine exhaust-gas temperature would be brought to what it should be, or to the level normal in the stabilized plant operation, as quickly as possible.
The control system, therefore, was designed to detect the engine output and turbocharger speed and control the gas-extraction valve open/close operations according to the deviation of turbocharger speed from what it should be for the engine steady-state output. In practice, the control system was designed on the feedback principle so that the gas-extraction valve would be activated to open when the turbocharger speed increased a certain rpm past the set point provided for the engine output and would determine the required valve open position from its deviation quantity and speed by PID action.
Fig. 8 shows the diesel generating plant configuration thus finalized. The gas-extraction valve was connected between the exhaust manifold and turbocharger turbine side and installed in the position where it bypassed SCR.
Fig. 9 shows the results of measurement taken of changes in turbocharger speed, engine exhaust-gas temperature, and gas-extraction valve open position that took place when the engine output was brought down from 3600 kW to 2600 kW.
Fig. 8 Finalized Diesel Generating Plant Configuration
