Читать книгу Maintenance, Reliability and Troubleshooting in Rotating Machinery - Группа авторов - Страница 24

The horsepower load on a centrifugal compressor is governed by the flow, gas density, the rotor geometry, and the rotational speed. For a given set of impeller diameters and gas conditions, the fan affinity laws define how flow, pressure, and the required horsepower vary as the compressor’s rotational speed changes as follows:

1 The flow rate varies directly with the speed

2 The differential pressure varies with the square of the speed

3 The power use varies with the cube of the speed

Small operating changes can have significant effects on how a compressor performs, which is why operators should carefully track the compressor’s overall operating characteristics, including the horsepower load, and look for trends indicating process changes. An overload condition may be telling you something is wrong. Overloading may be manifested by high amp loads for compressor with electric motor drivers or a loss of speed for compressors with gas or steam turbine drivers. If amp loads are seen to be rising or dropping, try to determine the cause of the change. Rising amp loads may be caused by changing process conditions or machine degradation, depending on the shape of the compressor performance curves. Falling amp loads may be caused by a decrease in flow due to a flow restriction or a decrease in the suction pressure.