Power generation plants rely heavily on demineralized and deionized water to maintain required levels of water purity during process operations. Managing the water supply is critical under normal operating conditions, as well during outages. The introduction of make-up water during normal operation and re-filling of the boilers after an outage can introduce contaminants that cause corrosion of components and damage to the boiler system.
Prevent corrosion with sparging and blanketing
To prevent corrosion from occurring in boiler feedwater tanks, nitrogen sparging and blanketing practices should be put into place. Sparging and blanketing, when combined, introduce high purity nitrogen into the water tanks and maintain a protective layer of nitrogen. In other words, nitrogen sparges the water to remove any dissolved oxygen and carbon dioxide (CO2), and the humid air in the head space is replaced by pure, inert nitrogen.
Sources of nitrogen
There are two ways for power plants to obtain nitrogen:
- Sourcing the nitrogen from an outside supplier.
- Generating the nitrogen on-site using standard compressed air.
Supplier sourced nitrogen
Nitrogen can be received from a supplier as a gas in high-pressure cylinders or as a liquid in micro-bulk tanks (dewars) and bulk tanks. Relying on outside vendors can pose several challenges including uncontrollable price increases, contract negotiations, rental fees, adherence to OSHA requirements, hazardous material fees, delivery surcharges, and local and state taxes. Problems such as scheduling conflicts, delivery delays, and lengthy procurement processes can slow down operations. Additionally, a gas delivery requires third party access to the power plant that could result in a security issue.
Nitrogen generated on-site
A cost-effective, energy-efficient alternative to obtaining nitrogen from an outside supplier is to produce it on-site with a nitrogen generator. An N2 generator uses pressure swing adsorption (PSA) technology to transform standard compressed air into high purity nitrogen. Payback may be realized in just two years or less. Making your own nitrogen uses less energy than traditional manufacturing at an air liquefaction plant.
A Parker PSA nitrogen generator, for example, produces compressed nitrogen at up to 99.9995% purity from nearly any compressed air supply. The system uses high-efficiency pre-filtration to remove contaminants down to 0.01 micron from the compressed air stream. The pre-filters are followed by dual pressure vessels filled with carbon molecular sieve (CMS). Parker’s nitrogen is system is compact allowing users to maximize floor space, and includes pre-filters, final filters, and a buffer tank. Simple installation involves connecting a standard compressed air line to the inlet and connecting the outlet to a nitrogen line.
Making nitrogen on site offers many advantages over outsourcing including cost savings, longer equipment life, continuous operation, elimination of safety concerns with handling high pressure cylinders, and freedom from the hassles of vendor management.
Read this white paper for more information on preventing contamination and corrosion in demineralized water storage tanks.
This blog was contributed by David Connaughton, product manager, Parker Hannifin Gas Separation and Filtration Division.