Screw compressor working principle and use in District Cooling

The chiller plant is one of the major systems of a district cooling plant. Others are the distribution network and the consumer system. The  compressor, which is the focus of this post, is a critical component of a chiller plant. ARANER is an experienced provider of District Cooling solutions. We can be trusted with help in choosing the right compressor type for a district cooling system. We will start with the basic screw compressor working principle. The compressor comes with both male and female rotors that can either drive each other or rely on a timing gear.  

Rotor operation process

Usually, the male rotor connects to the motor, acting as the driving rotor, while the female rotor is driven. As the two rotors rotate, volume in their grooves reduces thereby compressing the refrigerant. We could view the operation process in the following stages:

• First stage: the inlet port of the compressor takes the refrigerant.
• Second stage: tooth space reduces as the seal line goes in the direction of discharge. Compression takes place.
• Third stage: compression continues up to the point where both rotors are at the discharge port. Pressure is high at this point.
• Fourth stage: with the seal line at the discharge, the tooth space discharges the refrigerant

Fig 1: Rotary Screw Compressor in Sectional View

Types of Screw Compressors - Reason to Choose Carefully

Searching for a suitable screw compressor is daunting for cannot differentiate screw compressor working principles. Interestingly, screw compressors are either single-screw or twin-screw type.  

Single-Screw Compressor

The single screw compressor comprises of two gate rotors and a main rotor. The main rotor, which is the driving rotor, meshes with the gate rotors to produce the compression process.

Twin-Screw Compressor

Unlike the single screw compressor, the twin-screw compressor comes with helical grooved two rotors. As the two mesh, fluid flows in the axial direction. This compressor is very common in commercial and industrial applications.

Screw Compressor Parts and Applications

The parts of the screw compressor

The screw compressor is a positive displacement machine that comes with two helical lobed rotors that mesh as indicated in Figure 1. The two rotors in a casing create working chambers that are the basis of the operation of a screw compressor. We can categorize the parts as follows:

1. Rotor

There are two rotors, the male and the female rotors. Normally, the female rotor is bigger than the male rotor. It is also driven by the prime mover and consequently it rotates the male rotor.

2. Suction Valve

This is the section of the compressor where gas control takes place.Set at the inlet of the compression chamber where it’s possible to catch and reduce dust, and ingress of damaging particles. Necessary for cleaning and protection of the compressor stage/s. It can be controlled pneumatically or electrically.

3. Prime Mover (typically an electric motor)

The compressor draws its power from the electric motor or any other prime mover depending on design. You can also expect to find different power transmission systems with different manufacturers and models.

4. Oil Section

It comprises of the oil tank, oil filter and oil separator.   As you can expect from the categorizations, the screw compressors features many precision parts. These include couplings, gears, plungers, housings and belts. For advanced efficiency, the device also comes with an air receiver for buffering and storage applications between the compressor and the consumption system. The receiver is further categorized as primary receiver and secondary receiver. The screw compressor also features the air dryer whose role is to remove water vapor from the air. This prevents serious operational problems in the system including process obstruction and corrosion. Below are other parts of the screw compressor refrigeration system, some of which are visible in Figure 1.

• Screw(s)
• Rotors
• Intake port
• Discharge port
• Oil separator
• Slide valves

Applications of the Screw Compressor

The screw compressor is a critical component in many industries that ARANER deals with. In the food processing industry, the product is important in food cooling, pressurized transport and agitation. The product also features in pharmaceutical facilities where it is used in packaging, aeration and pill manufacturing. In summary, the machine is common in the following other industries:

1. Civil engineering and construction
2. Machinery
3. Pulp and paper
4. Electronics
5. Automobiles
6. Theme parks

Benefits of Screw Compressor

Many industries use the screw compressor because of ease of maintenance, overall economy and simplicity. The compressor has been lauded for its high specific output, which is crowned by the usually small size of the devices. Maintenance is flawless thanks to the few parts. With new technology, you can expect a screw compressor to run efficiently also.  

Fewer parts means minimal vibration, which is another reason district cooling establishments should install these compressors. Do not forget that refrigerant loss is almost non-existent for these products. With input from an experienced player such as ARANER, you can confidently use a screw compressor for your district cooling and other industrial applications.  

Keep reading: Industrial Process Refrigeration: An In-Depth look at each component

ARANER’s contribution

Choosing the right screw compressor is important, as it will save you money and lots of trouble. Where are you planning to use the compressor? Contact ARANER and get all the guidance necessary for optimum service from a screw compressor.

ARANER offers complete screw compressor maintenance solutions to help facility owners focus on core business. From preventive maintenance to breakdown repairs, replacements and retrofits, ARANER can handle all these reliably so that the customer can enjoy the full benefits of their district cooling system The aim of our services and products is to enhance the efficiency and life of the compressor.

Customers enjoy reduced operating costs thanks to our detailed compressor performance analysis and concrete documentation. Our success in these solutions is attributed to focus on specific client requirements. Now we must mention that we offer various types of maintenances such as preventive, breakdown and scheduled.

Maintenance of screw compressor unit

When it comes to maintenance of a screw compressor, focus is obviously on the parts. How many parts do you have to consider? A screw compressor has very few major parts (only 4)-oil components, suction valve, air-end and electric motor. This is a plus in terms of maintenance, as very little is required.This is a plus in terms of maintenance, as very little is required. Vibration can also be a problem in a district cooling plant, and special equipment is needed to control it.

Fortunately, for a screw compressor, vibration is minimal so this cost is avoided. Even with these limited vibrations, it is still necessary to ensure that all fasteners are tight. Check the bolts, screws and nuts on a regular basis and tighten them in case they are loose. This equipment has internal moving parts that need attention. Remember that compressor oil plays multiple functions-lubrication, cleaning and cooling. Scheduled change of the oil is important because without that the equipment can be damaged. A compressor’s screw element is designed to last about 40000 hours.

However, reaching this longevity is not a guarantee if the following issues are not handled-vibration, overheating, condensation and poor lubrication. To prevent premature failure of the equipment, check for bearing noise and oil leaks, and call a professional if there is a problem. In summary, here are a few important maintenance activities for the equipment:

• Checks for water and air leaks
• Weekly checks for oil condition
• Weekly inspection and cleaning of filters
• Removal of debris and dirt from unit exterior

Screw compressors are increasing in popularity, but many people still have scanty knowledge about screw compressor working principle and the importance if this equipment in district cooling. We have highlighted the basics of screw compressor types, their operation, their maintenance and the role ARANER plays in this area. Screw compressors are a significant part of the company’s solutions. If you enjoyed this post you may be interesting in  refrigeration compressor types: which is the best solution.

If you would like to learn more about the operation and applications of screw compressor in relation to district cooling, and to select a suitable one, do not hesitate to contact ARANER.