JB/T 6443.4-2006Axial and centrifugal compressors and expander-compressors for petroleum chemical and gas industry services - Part 4: Expander-compressors (English PDF)

1.1 Scope

This part, together with Part 1 of this standard, specifies the minimum requirements for process air or gas expander-compressors. This part applies only to units in which the expander and the compressor, abbreviated as the expander-compressor, have a common shaft.

This part does not apply to expanders with a separate output shaft, such as those driving a generator.

Hot gas expanders operating at temperatures above 300 degrees Celsius (570 degrees Fahrenheit) are not covered by this standard.

1.2 Terms and definitions

The definitions of the terms used in this part are already given in Part 1 of this standard. Sectional views showing the terms used for expander-compressors are given in Annex 4C.

2.1 Basic design - General

Expander-compressors shall comply with 2.1 of Part 1 of this standard and with the additional requirements below.

2.1.1.1 The predicted efficiency of the expander at the normal operating point shall reach at least 98 %. Under normal operating conditions the power consumed by the compressor shall be not more than 106 % of the power delivered by the expander, and not less than 96 % of it.

Note: because the power consumed by the compressor depends on the power delivered by the expander, this is what fixes the speed of the compressor. The tolerance above is only a limit; where it is exceeded, hardware has to be changed in order to reach a reasonable normal speed.

2.1.1.2 The head-capacity characteristic curve of the compressor shall rise continuously from the rated point to the surge point. With no bypass, the compressor shall be suitable for continuous operation on the predicted performance curve at any flow at least 10 % greater than the predicted surge flow given in the quotation.

Note: during normal operation the compressor usually works with a gas recycle bypass.

2.2 Materials

Materials shall meet the requirements of 2.2 of Part 1 of this standard. A table of typical materials is given in Annex 1D.

2.3 Casings

Casings shall meet the requirements of 2.3 of Part 1 of this standard and the additional requirements below.

2.3.1.1 The purchaser shall specify the set pressure of the relief valve of the system. The maximum allowable working pressure of the casing shall be at least equal to the set pressure of the relief valve.

2.3.1.1.1 Where the set pressure of the relief valve is not specified, the maximum allowable working pressure of the expander casing shall be at least 1,1 times the maximum specified inlet pressure, gauge.

2.3.1.1.2 Where the set pressure of the relief valve is not specified, the maximum allowable working pressure of the compressor casing of the expander-compressor shall be at least 1,25 times the maximum specified discharge pressure, gauge, but not less than the maximum discharge pressure specified in Part 1 of this standard.

Note: the pressure protection device of the system is to be supplied by the purchaser.

2.3.1.2 The O-rings, gaskets or other sealing devices commonly used on vertically split casings shall be confined in machined grooves, and the O-rings, gaskets and other sealing devices shall be made of a material suitable for the specified service conditions.

2.3.1.3 Means shall be provided for lifting the casing and for removing the centre section.