Reducing Costs, Maintenance and Downtime Risk with Liqui-Cel® Membrane Contactors
Historically vacuum towers, steam deaerators, decarbonators and chemical injection were common methods used to control dissolved oxygen and carbon dioxide in make-up and feed water to power plants, Heat Recovery & Storage Generators (HRSGs) and other plants with boiler water systems for producing steam. However, these methods can be much less efficient, require more maintenance and the handling of large volumes of chemicals. Liqui-Cel Membrane Contactors used for deaeration can reliably achieve very low dissolved gas concentrations and can operate much cleaner compared to alternative degassing methods using much less space.
Controlling dissolved O2 and CO2 levels in boiler make-up and feed water systems is critical to plant operation Both of these gasses are corrosive and can negatively impact boiler performance and corrode metals in contact with the boiler feed water such as economizer heat exchange surfaces. CO2 that exits with the steam forms carbonic acid as steam condenses and significantly lowers the pH of the condensate which is a major source of acid attack that can cause early piping and component failure.
The corrosion products that result can deposit and plug small process devices. This plugging can cause significant process heating control and product quality issues. The corrosion products can also be transported back to the boiler in the recovered condensate and contribute greatly to boiler water conductivity. This causes higher blow down rates which translates to higher water and energy costs for the plant. Additionally, fouling of the boiler heat exchange surfaces with corrosion products lowers operating efficiency and puts tubes at risk of failure. Installing Liqui-Cel Contactors in make-up or feed water systems can alleviate corrosion from dissolved gasses to reduce costs and improve operating efficiency.
Injecting oxygen scavengers after the steam deaerator to remove any remaining dissolved oxygen is also a common practice. However, during periods when the steam deaerator is not available large amounts of scavengers are needed. This is expensive, hazardous and contributes to conductivity/TDS in the boiler water. Using high volumes of chemicals can mean lower cycles of concentration of the boiler water and a corresponding higher blow down rate, which leads to higher make up water use and higher energy losses.
Oxygen removal down to 1ppb can be achieved with membrane contactors. Compared to a typical vacuum tower or steam deaerator that can only achieve 7ppb, this can significantly reduce the amount of oxygen scavenger used during normal operations and alleviate the need for high dosing when the deaerator is not available. Because the achievable oxygen levels are so low with a Liqui-Cel Membrane Contactor system, the steam deaerator can be used as a feed water preheater and storage instead of venting off the dissolved O2. A plant can realize significant cost savings by reducing the deaerator vent rate. In many cases, realized savings can be up to 1% of the total annual fuel cost!
Membrane Contactors are extremely attractive to the many industries that rely on boilers for power and process steam. Membrane Contactors are very efficient with 10 times more surface area compared to most vacuum towers. Since they are very small and compact, the skid can be installed inside with a minimal footprint. Installation near the boiler requires less piping and has lower installation costs. Membrane contactors can be run in-line and under pressure. Because there is still positive pressure at the outlet of a Membrane Contactor system, represssurization/booster pumps can also be eliminated.
Find out how you can lower costs and improve efficiency at your plant by using Liqui-Cel Membrane Contactors. Contact us to discuss your application today.
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