Because liquid CO2 must be transferred at a controlled combination of low temperature and high pressure to minimise vapour forming, pumping liquid carbon dioxide presents an array of challenges to process engineers. For the pump manufacturer, the inherent compressibility and poor lubricating properties places special demands on pump design.
Cat Pumps has met these challenges by developing a high pressure positive displacement plunger pump specifically for handling liquid CO2. The ‘1951’ plunger pump provides users with the ability to lower running costs, reduce maintenance and eliminate the requirement for extra cooling or an additional booster pump. In keeping with similar Cat pumps which offer flowrates of up to 120l/m and pressures up to 350 bar, the key to the economic and efficient operation of the Cat 1951 is its optimised unswept volume, which means that only a small volume of liquid CO2 is compressed during the pumping cycle. Not only does this result in less energy being added to the liquid stream, it also means that the liquid is not heated unnecessarily, energy consumption is reduced and the pump can run slower for a given flow rate.
Having a flow rate of between 1 and 19 l/min, the Cat 1951 pump delivers consistent flow at pressures up to 100 bar as well as accommodating a high inlet pressure (up to 60 bar). As a result, the liquid CO2 can feed directly from the storage tank and can be pumped close to ambient temperature. The presence of a large, smooth top-inlet arrangement eliminates any regions where vapour could be trapped. The pump cylinders receive only liquid and not a gas-liquid mixture because any entrained gas bubbles are vented back to their source allowing the pump to operate closer to the liquid/vapour transition.
The pump head is manufactured UNS 31603 stainless steel for liquid and process compatibility, strength and corrosion resistance. The concentric, high density polished ceramic plungers are abrasion resistant, providing excellent seal life. The plunger seals are lubricated by the liquid CO2, so there is no requirement for additional seal flushing liquids but the seal arrangement can be configured to allow early detection of seal deterioration prior to routine servicing.