GENERATOR AUXILIARIES (GAS SYSTEM ) PART-III ABC OF THERMAL POWER PLANT

GAS SYSTEM: Generator is cooled by introducing H2 gas as coolant. Heated H2 gas is cooled on Hydrogen cooler attached with generator. Primary water cooler and Hydrogen Cooler is cooled by DM water supply from the system either from CEP discharge or closed loop ACW system.

Use of H2 gas needs special attention because if it mix with air it may explode. Therefore safety precaution is paramount in case of Gas system. No half measure to be taken during erection and commissioning of the system. Only experienced personal should handle the system with safety precaution. I will outline the gas system required for the generator in brief.

The gas system consists of the following components:

- CO2 cylinders

- H2 cylinders

- N2 cylinders

- Gas dryer

-Gas valve manifold

Hydrogen Gas with Purity of 99.7 % minimum is charged from the cylinders to the manifold . The cylinder pressure is much higher than the required pressure . Therefore two parallel connected pressure reducing valves are used to take care of expansion.

As a precaution against explosive mixtures, air must never be directly replaced with hydrogen during generator filling not the hydrogen replaced directly with air during the emptying procedure. In both cases, the generator must be scavenged or purged with an inert gas, carbon dioxide (CO2) being used for this purpose.

CO2 is also supplied in liquid from and in compressed condition. During CO2 filling  temp control is necessary and is provided in the rack to save from excessive cooling.

To remove the CO2 from the generator,(during commissioning or on shut down) a compressed air supply with compressed air filter is connected to the general air system of the power plant. Under all operating conditions, except for CO2 purging, the compressed air hose between the filter and the generator pipe system should be physically disconnected. This is to avoid any contact with Hydrogen and air.

A gas valve rack is furnished with a mini diagram on the face of the panel to show the system . The valves used in the gas system have rubber/metal sealed valve seats to ensure gas tightness.

For measurement of Pressure transmitters are used. Also analyser , purity meter is also used in the instrument panel.

A small amount of the hydrogen circulating in the generator for cooling is passed through a gas drier. The gas inlet and gas outlet pipes of the gas dryer are connected at points of the generator with different static heads(differential fan pressure), so that the gas is forced through the dryer by the differential pressure only. Gas drier is electrically operated with temperature control.

A typical PID diagram is attached (BHEL make) below.

P.S If  you are looking to earn few extra money from the comfort of your home then please click on the link given below

LINK 1 - PLEASE CLICK HERE 
LINK 2 - PLEASE CLICK HERE