Compressor cylinders have the ability to generate a lot of heat and reach high temperatures. To avoid a dangerous situation, it’s crucial to learn about the role of cooling systems.
Compressors such as reciprocating compressors generate heat during their working cycle as a result of compression transformation and friction of moving parts. This heat can lead to an increase in the gas discharge temperature and a reduction in volumetric efficiency.
On the other hand, cooling systems are used in compressor cylinders to ensure that there is no excess heat. Also, a proper design of the cooling system is made to provide a balance between the refrigerating potential and system capacity.
What are Compressor Cylinders?
Compressor cylinders are pressure vessels that hold the gas during the compression cycle. There are single-acting compressors that compress gas in just one direction of piston travel – and they can be a head end or crank end.
On the other hand, double-acting cylinders compress gas in both directions of the piston travel, and a good number of reciprocating compressors take advantage of double-acting cylinders. That aside, here are some things to know about compressor cylinders and cooling.
1. Cylinder Cooling Systems are Essential in Compressors
When power is passed through a compressor, it is converted to heat during the compression process.
However, this heat is removed from the compressor using a cooling system for a number of reasons.
These reasons include:
1. To enhance the efficiency of multistage compressors. This is made possible through an increment of the density of air between stages of compression.
2. To ensure that the compressed air and various compressor parts do not reach extremely high temperatures.
To that effect, compressor cylinders are cooled by passing freshwater or seawater through them. The water is then circulated through the cooling water passages in the cylinder block. Therefore, cooling systems are essential in the proper functioning of compressors.
2. Compressor Cylinders are of Various Types
There are various types of compressor cylinders, and they are described by the presence or absence of cooling water jackets.
These compressor cylinders include:
– Water-cooled Compressor Cylinders:
Heat is usually created as a result of gas compression and friction. And as such, traditional compressor cylinders are generally designed with cooling water jackets. These water-cooled cylinders help in the uniform distribution of generated heat, which brings about immense benefits.
Some of these benefits include reduced suction gas preheat, prolonged parts life, cylinder lubrication, as well as a reduction in maintenance.
– Non-cooled Compressor Cylinders:
There are also non-cooled compressor cylinders, and in the last 30 years of their operation, they have performed without cooling water jackets. These operations have been successful in a good number of natural gas compression applications. And like water-cooled cylinders, there are several advantages of non-cooled compressor cylinders.
A significant advantage of these systems can be tied to their simplified designs that bring about reduced cost while setting them up. Their design also offers a lower initial system costs as a result of reductions in the cooling water system, reduced weight, and improved valve accessibility.
Despite the benefits provided by non-cooled compressor cylinders, some compressors are still supplied with liquid coolants.
3. Liquid Coolant Systems
Cooling jackets in static systems are usually filled with a mixture of glycol and water in a bid to provide uniform distribution of heat within the cylinder. Similarly, this system may be employed where the gas’ AT and discharge temperatures are less than 150°F and 190°F, respectively.
On the other hand, thermal siphons establish a flow by using the differences between the hot and cold coolants. A system of this nature may be used where AT of the gas and discharge gas temperature are less than 150°F and 210°F.
4. Forced Coolant Systems
Forced coolant systems that rely on glycol and water are the most common for natural gas compressors. In this case, there is a combination of the compressor cylinder cooling system and the compressor frame lube oil cooling.
Circulation of the coolant through the cylinders and the lube oil heat exchanger are carried out using a single pump. The coolant is then sent to an aerial cooler where the heat is dissipated.
On the contrary, caution is required when forced coolant systems are used. Here, there is a need to ensure that the right coolant temperature has been provided.
The right temperature would be one where the coolant temperature is limited to less than 30°F above that of the suction gas. This is because if the cylinder is too hot, there is a loss in gas throughput capacity as a result of gas heating and expanding. Likewise, if the cylinder is too cool, there could be a condensation of liquids from the suction gas stream.
5. Factors that Determine the Size and Type of Cooler Used
In the end, certain factors determine the size and type of cooler that is used in a compressor.
A major factor is the amount of heat that is required to be removed from the oil that absorbs the heat. This is referred to as “heat rejection,” or “heat load.”
The requirements of the frame oil heat rejection may vary in terms of compressor speed, size, and ambient conditions.
6. Requirements When Using Cooling Water in Cooler
The cooling water that is supplied to the cooler should be clean with an antifreeze additive. The aim is to provide maximum service interval.
Similarly, it is essential to regulate the cooler water flow to ensure that the oil temperature is maintained at a minimum of 130°F (54°C). Over and above that, the cooling water temperature to the cooler should not exceed 150°F (86°C) irrespective of the circumstance.
Conclusion
Compressor cylinders need to be cooled to ensure the proper functioning of the compressor parts, especially when consideration is given to the heat that is produced by these machines. Much more, a lot of processes are involved in this cooling process to ensure that the compressed air does not have an extremely high temperature.
That being the case, cooling systems within compressor cylinders come with significant benefits that give them an edge over other systems out there. Manufacturers have found a need to stillincorporate them in compressors due to these benefits and more.
