The purpose and significance of the balance section in reciprocating compressors

A differential compressor is used to balance the piston thrust.

This post was last edited by jffly on 2010-6-16 08:24. The balance section of a piston compressor refers to the single-acting cylinder in which only one side performs effective compression work as the piston moves back and forth; the other side forms a passage with low-pressure gas, and this is the balance section. This design was adopted around the 1960s because, given the low level of productivity at that time, it was difficult to manufacture large piston compressors with high piston forces. Therefore, a structure with a balance section was used to reduce the piston force. Additionally, since the technology for manufacturing high-pressure seals was not available at that time, a structure with a balance section along with low-pressure cylinders connected in series on the shaft side was employed, so as to use only medium- and low-pressure seals. However, this structure achieves the aforementioned objectives at the cost of increased energy consumption. Since the balance section is connected to the low-pressure gas, this gas undergoes repeated and ineffective compression within the balance section, resulting in unnecessary energy waste. Meanwhile, the gas that leaks from the high-pressure side into the balance section through the piston rings returns to the low-pressure stage to be compressed again, further increasing energy consumption. Moreover, the gas leaking back from the high-pressure side to the balance section is hot gas generated during compression; as this gas returns to the cylinders of the low-pressure stage via the balance section, it raises the inlet temperature of those cylinders and causes them to expand, which in turn reduces the amount of air drawn in by the low-pressure stage cylinders. As a result, the amount of gas produced is reduced, failing to meet the designed output level. As the compressor industry continues to introduce, assimilate, and adopt advanced foreign technologies, especially the successful use of high-pressure sealing gaskets and piston rings, it becomes possible to use stepped cylinders without balance sections as well as double-acting cylinders in the high-pressure section. This prevents high-pressure gas from leaking into the low-pressure section, while also improving the sealing pressure difference of the piston rings. The forces acting on each row of pistons become more balanced, and due to reduced gas leakage, the volume of gas processed by the compressor increases. As a result, its output far exceeds that of other compressors with balance sections under the same operating conditions, At the same time the power consumption of the compressor is significantly reduced as well. Modern new technology compressors employ a technology that eliminates balance sections; each cylinder is a double-acting cylinder. During its reciprocating motion, each piston moves independently. There are no balance section cylinders between the cylinders of the same row, and the cylinders of different stages in the same row are arranged in a series double-acting configuration, an inverted stage difference configuration, or a combined series configuration. This compressor not only offers significant energy savings and a substantial increase in output, but also operates smoothly. Taking the 4M8 type compressor used in nitrogen fertilizer plants as an example, upgrading it with this technical solution can result in energy savings of 8–10% and an increase in production of over 5%.