【2025 Safety Design】Key Points for Valve Settings of Compressors

I. Installation of isolation valves and blind flanges 1. Except for air compressors that draw air from the atmosphere and therefore do not require an inlet valve, all other compressors need to have isolation valves at both the inlet and outlet. This is to effectively control the airflow during normal operation, facilitating the isolation of the compressor.

2. For compressors that may require maintenance during operation, blind plates in the shape of an “8” should be installed on the inside of the inlet and outlet. Blind plates provide reliable isolation during maintenance, preventing gas leaks and ensuring the safety of maintenance personnel.

II. Installation of bypass pipelines and connecting valves 1. A bypass pipeline should be installed between the inlet and outlet valves of the compressor, along with connecting valves. The bypass line of a reciprocating compressor can reduce the load during startup, disconnects from the system during testing after maintenance to prevent pressure buildup, and maintains positive pressure at the inlet when handling explosive gases. The bypass circuits of multi-stage reciprocating compressors are connected stage by stage, which helps save energy and ensure balanced operation of each stage; if necessary, a bypass can also be installed between the final stage and the inlet. The bypass capacity of the centrifugal compressor must be at least equivalent to the load at the surge point.

2. The air compressor only requires a direct atmospheric outlet equipped with a shut-off valve upstream of the outlet valve, in order to release gas when necessary and prevent excessive pressure.

III. Valve settings in auxiliary systems 1. Cooling water system: The cooling water can be used in series according to temperature requirements, starting with the pre-cooler and then moving on to the cylinder jacket. A shut-off valve is installed at the inlet of each cooling water circuit, and corresponding measures are taken at the outlet. The normal-pressure return water outlet is positioned above the upper edge of the return water funnel; a sight glass is installed at the pressure return water point, and a shut-off valve is provided at the pressure return water outlet. The outlets of different units on the same equipment can be combined and then equipped with a single shut-off valve. These valve settings ensure proper circulation of cooling water, facilitating observation and maintenance.

2. Lubricating oil, seal oil, and flushing oil systems: When the compressor’s product documentation does not specify the inclusion of these oil systems, pipes and valves must be installed as required. Important areas such as bearings should have separate lubrication circuits to ensure proper lubrication and sealing of the equipment.

3. Drain valves for separation tanks: Drain valves are installed in the separation tanks between various stages of the compressor. The pressure drop is taken into account when the liquid is discharged into the main pipeline, to ensure that the pressure in the main pipeline remains lower than the pressure at each stage. Check valves are installed at the outlets of the liquid from each separation stage to prevent backflow and ensure the proper operation of the system.

Selection principles for centrifugal compressors: Centrifugal compressors are primarily composed of components such as the rotor, stator, and bearings. An electric motor or steam turbine drives the impeller to rotate, enabling the gas to acquire kinetic energy within the impeller, which is then converted into pressure energy, thereby achieving the compression and transportation of the gas. Centrifugal compressors feature a compact structure, stable operation, high efficiency, and large flow rates, but their pressure ratio is relatively low, making them suitable for operation in medium and low pressure ranges. The selection principles are introduced below:

1. The seller shall calculate the specific heat capacity, compressibility factor, and other gas property parameters required for compressor design, based on the given gas composition. 2. The unit’s performance must meet the requirements and enable it to operate continuously and safely under specified conditions. Its service life is at least 20 years, with an expected period of uninterrupted continuous operation of at least 5 years. 3. For variable-speed compressors, the seller shall ensure that there is no negative tolerance for flow rate and head under rated operating conditions, with an axis power tolerance within the range of +4% to 0%. For compressors with a fixed speed, the seller shall ensure that there is no negative tolerance for flow rate under rated operating conditions; the head tolerance is +5% to 0% of the head at the normal operating point, and the shaft power tolerance is +7% to 0% of the value at the guaranteed point. 4. The pressure-flow performance curve of the compressor should rise continuously from the rated point to the surge point.

5. The design pressure of the casing shall be at least equal to the sum of the highest suction pressure and the maximum pressure rise that may occur when the compressor is operated under the most severe combination of all specified operating conditions at the tripping speed, or equal to the safety valve setting specified by the buyer. 6. Unless otherwise specified, the casing shall have a vertically split structure when the pressure exceeds 3.923 MPa (gauge) or when the hydrogen partial pressure exceeds 1.38 MPa (gauge). 7. Replaceable labyrinth seal elements should be installed at all internal sealing points to reduce internal leakage. Priority should be given to stationary, easily replaceable labyrinth seals.