2G GAS BLENDING SYSTEM

Transcription

1 2G GAS BLENDING SYSTEM System Overview The gas blending system blends natural gas with biogas for operation of CHP. The mixture ratio of natural to biogas gas is determined by gas level/pressure in the digester/biogas system. The gas level/pressure is continuously monitored by the gas blending system via an analog input (4-20mA) signal supplied by customer. Normal Operation (Biogas Only) When the biogas level/pressure is high enough to sustain CHP operation the gas blending system is in normal mode. Solenoid valves for both biogas and natural gas are opened. The throttle valve for natural gas is closed. No natural gas will be added. Power output of the CHP is adjustable between % rated load, based on biogas level/pressure and percent of power commanded. Biogas consumption data is measured by a flow meter installed in biogas supply line. Gas Blending Operation (Biogas + Natural Gas) Should the gas production be lower than the consumption of the CHP, the gas blending system will then add natural gas to the consumed biogas of the CHP by opening the throttle valve in the natural gas line. The throttle valve works as a pressure limiter for the natural gas and is controlled by a PID regulator. By opening the valve, the natural gas pressure behind the fuel blending system increases which allows regulation of the natural gas consumption. The flow meters installed on the system continuously measure the consumption of both gases. The gas blending starts when a set gas level/pressure has been reached in the digester; this setting can be adjustable by the customer. The gas level/pressure for starting the gas blending process is adjustable via the touch panel of the CHP. Range for mixing operation is up to 70% natural gas content of the overall heat input of the CHP. Natural Gas Operation Should he mixing ratio be higher than 70%, the PLC will automatically power down the engine and switch engine settings to natural gas operation, which includes different combustion curves for lambda setting and optimized gas mixer positions for starting sequence. Power output for natural gas operation can be set manually via the touch panel. (This scenario will only happen when no biogas is available or operator wishes to operate on 100% natural gas). Automatic switchover to 100% Natural Gas mode can be disabled on the HMI. The system would then inject max. 70% natural gas, depending on gas level. 1

2 Figure 1 Control page to set mixture ratio and CHP power output depending on gas fill level/pressure as well as set point value for natural gas operation and back to mixing operation. P&ID page to display actual values as for example natural and biogas pressure, flow rates for both natural and biogas, throttle valve position and gas fill level/pressure. 2

3 Data page PLC menu 3

4 Analogue inputs Digital inputs and outputs 4

5 Trend log for all analogue inputs and outputs Bill of material for gas blending system: - Skid for gas blending system (only for building applications) - Throttle valve for natural gas - Gas train for biogas: o 2 solenoid valves o Debris Filter o Leak Test System - Gas train for natural: o 2 solenoid valves o Debris Filter o Leak Test System - Flow meter for biogas - Flow meter for natural gas - Pressure sensor for incoming natural gas pressure - Pressure sensor for incoming biogas pressure - Special designed mixing unit for high turbulence mixing of biogas and natural gas - Flame arrestor installed upstream of CHP 5