The first Thomassen C-85 reciprocating compressor with eight cylinders and a capacity of 16.6 MW was delivered within the challenging one-year deadline. The compressor is one in a series of six, the last of which will be delivered six months later than the first. The building of these compressors are a key milestone for a new generation of compressors that not only comply, but exceed the current API 618 (American Petroleum Institute) specifications and Shell DEPs (Design Engineering Practices).
Howden took the initiative to opt for six compressors with eight cylinders each instead of the initial seven compressors requested for KNPC. This was with the full backing of contractor Fluor.
Before arriving at the choice of six rather than seven compressors, various options with six and seven compressors and six to eight cylinders were examined by Howden and Fluor in terms of their feasibility and suitability for the project.
Niek Albers, Manager of Technology HTC explains why the final decision of opting for six compressors with eight cylinders was taken: "Although a combination of six reciprocating compressors with this capacity had never been realized, Howden already had the design for an eight-cylinder compressor frame on paper, and we had experience in integrating larger numbers of parallel compressors. The creation of the frame for an eight-cylinder compressor is an innovation that began some time ago at Howden. Making the final choice to go with six compressors with eight cylinders was based on attempting to achieve the highest efficiency and greatest flexibility in regulating capacity."
Niek also outlines the robust and thorough planning that went into this highly complex project: "Since the C-85 compressor with eight cylinders had never previously been built, we made detailed calculations prior to the award of the project by Fluor. For these compressors, specific attention was placed on the preliminary phase, investigating aspects such as torsional vibrations and pulsations. This enabled Howden, in collaboration with Fluor, to identify the critical issues early on and come up with concrete solutions; guaranteeing the reliability of the compression system.
That reliability is an absolute prerequisite for a project where system downtime can cost millions of dollars. This preliminary thoroughness and collaboration with Fluor meant we could make robust choices concerning the design, such as the optimum load per machine, and creating a flexible but easily adjustable capacity for each of the different compressors." Given the considerable number of possible combinations of operating compressors, regulating the capacity is a complex matter. In theory there are around ten thousand possible combinations to regulate capacity: all five machines in operation (with one machine on standby) can be adjusted to loads of 0%, 25%, 50%, 75% or 100%.