EMERSON'S ADVANCED GAS ANALYZER TECHNOLOGY PROVIDES ON-LINE ANALYSIS OF HYDROGEN COOLED GENERATORS
06 February 2007 - Emerson Process Management

The on-line thermal conductivity TCD analyzer is typically set up with three measuring ranges. The first and primary range (80-100% H2) is to monitor the hydrogen purity during normal operation; the second (0-100% H2) and third (0-100% CO2) measuring ranges allow safe opening of the turbines for maintenance.

On-line gas analysis is used to maintain a high concentration of hydrogen coolant to ensure cooling efficiency and maintain safe conditions. During normal operation, the hydrogen purity is monitored in an 80 to 100% H2 range (with air as background gas) to expose air leaks or hydrogen supply problems.

Keeping the hydrogen as pure as possible is critical for the efficient operation of a turbine. Every 2% reduction in the purity of the hydrogen coolant increases windage losses in the turbine and the cost of running an 800-megawatt generator is increased by up to US$1,000 a day. Contaminants in the hydrogen can also be very dangerous and air is the most common impurity due to leaks.

When the oxygen in the air is mixed with hydrogen, this can create an explosive condition. However, hydrogen does not support combustion in a nearly pure state (>90%) with the balance of air. By using the Rosemount Analytical CAT 100 continuous gas analyzer transmitter to constantly monitor the hydrogen purity, a potentially hazardous condition can be avoided, enhancing safety and maximizing efficiency and profitability.

When the turbine needs to be opened for maintenance, the hydrogen is first replaced with inert CO2 and this process is tracked with the second measuring range in the analyzer, 0-100% H2 (with CO2 as background gas). Once all of the hydrogen is removed, air is injected to displace the CO2 and this is tracked with the third measuring range 0-100% CO2 (with air as background gas). When all of the CO2 has been replaced with breathing air, it is safe to open the turbine. To restart the turbine, this process is reversed.

By accurately determining when each purge cycle is complete, the Rosemount Analytical CAT 100 continuous gas analyzer transmitter minimizes down time. Plant safety can be enhanced by ensuring that the right conditions exist before personnel can open the turbine for maintenance.

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