Development of mechanical seals for high-pressure CO2 applications

A mechanical HVAC seal usually rotates at 1800 rpm. However, in Brazil a high-pressure mechanical seal suitable for every phase of CO2 (gas, liquid, and supercritical), for dynamic rotation of 3600 rpm, and for pressures up to 500 bar has been developed.

High pressure CO2 offers unique design challenges for HVAC&R system development, particularly with regard to seals. A recent article in “fator Brasil” highlights the latest developments in the field of mechanical seals suitable for high-pressure CO₂ applications, used in to minimise leaks from pumps and compressors.

Designed for enhanced oil recovery; lessons for HVAC&R industry

The innovative high-pressure mechanical seal technology is suitable for every phase of CO₂ -gas, liquid, and supercritical. It was originally designed for the enhanced oil recovery industry, but could provide lessons for the HVAC&R industry.

The company that devised the seal, German company EagleBrugmann, believes the technology is the first of its kind. The new seal has been rigorously tested and is based on the API 53B for closed loop circulation of coolant and refrigerant.

Sealing technology: critical to CO₂ containment

Among all the refrigerant fluids currently used carbon dioxide (CO₂) has one of the widest application ranges, suitable for low temperature freezer plants at -50°C and hot water heating systems at 80°C in sizes from small domestic units up to huge industrial facilities. However, the temperature and pressure range involved in CO₂ refrigeration cycle limits the choice of seal materials and type of seal. The development of appropriate sealing technology has been critical to refrigerant containment of high-pressure CO₂.

For the optimal performance of refrigeration systems, including CO₂ systems, maintaining refrigerant charge is critical. Refrigerant losses can occur through pipe fracture, poor mechanical and brazed joints, through worn seals, and is occasionally vented through pressure relief valves. Proper operation requires that all components of a CO₂ system, including the seals, be designed to withstand high pressures over the entire system lifetime.

Background: functional components of mechanical seals

Mechanical seals prevent liquid or gas from escaping where the rotating shaft exits the pump or compressor housing and have proven to be reliable for the HVAC&R industry. Mechanical seals must contain four functional components:

Primary sealing surfaces: these are central to the mechanical seal and consists of two rings in intimate contact, with one ring rotating with the shaft whist the other ring is stationary;
Secondary sealing surfaces: these are other points in the seal that require a fluid barrier but are no rotating relative to one another;
A means of actuation: an actuation force is required to keep the two primary sealing surfaces in intimate contact;
A means of drive: to ensure that only the primary sealing surfaces are permitted to rotate relative to each other a method of drive must be provided.