Optimization of Propane Compressor Capacity and Flow Rate in Refrigeration System

Plant X requires pressurized gas in the refrigeration system unit, which plays an important role in the smooth operation of the production system. This is because propane gas is used as a support for the main operating system in the manufacture of LPG. More precisely as a cooling medium for tools called Chiller and Sub-Cooler. To obtain the pressurized propane gas, a screw compressor type positive displacement compressor is used. Propane Compressor C-440 A has a function, namely to circulate propane gas which is used to cool or lower the temperature of hydrocarbon gas. Considering the important role of the Propane Compressor C-440 A screw compressor, it is necessary to optimize it to determine

Page 1322 of 1327 the performance of the compressor.Optimization steps need to be carried out to find the most effective and efficient operating conditions.By lowering the suction temperature and increasing the rotational speed of the rotor.The reference parameter is that the targeted capacity has increased by 9%, resulting in the actual calculation of 30614.40cfm and optimization of 30902.03cfm.The mass flow rate is targeted to increase by 4%, resulting in an actual calculation of 627.92 lbm/min and an optimization of 654.80 lbm/min.With this, it can be calculated that the economic value is 26.89 lbm/min.

INTRODUCTION
Compressors are vital equipment in industrial processes and require special maintenance and operation so that their performance remains good.In Industry X, it uses a Positive Displacement Compressor, more precisely a rotary compressor type screw compressor.Which uses pure propane feed and injected lube oil as a lubricant, operates at high speeds, and produces higher output as well.Its main function is to compress/increase pressure and increase temperature, which later this refrigeration process is used to support the main process, namely as a cooling medium in Gas Chiller and SubCooler.So it has a very important role in the gas production process at the plant (Kovacevic et al., 2007).
With the following problem formulation, how to evaluate the compressor based on calculations using the parameters of inlet air pressure, inlet air temperature, and outlet air pressure.How to optimize compressor performance with calculation parameters, volumetric efficiency, capacity, mass flow rate, and power on the compressor.By lowering the suction temperature and increasing the rotation speed of the rotor (Borremans, 2019).
The hypothesis that can be determined as follows, namely Theoretical volumetric efficiency based on calculations is smaller than actual, this is influenced by the age factor of the tool.The longer the operation, the lower the volumetric efficiency.The theoretical capacity based on calculations is smaller than the actual.This capacity is influenced by the size of the volumetric efficiency.Lowering the suction temperature can increase compressor capacity by about 9% of the actual data.Increasing the rotational speed of the rotor can increase the capacity and mass flow rate by about 4% of the actual data because it strengthens the suction power of the compressor (Brown, 1997).
The goal to be achieved is to know the working mechanism and system of the Propane Compressor in the Refrigeration System in Industry X. Can compare compressor performance during new conditions with current operating conditions (Wang et al., 2013).Can determine the performance calculation parameters on the screw compressor to get a percentage/recap of overall efficiency data from the compressor itself.Evaluate the performance of the Propane Compressor in the Refrigeration System using the calculation parameters of volumetric efficiency, mass flow rate capacity, and power used so that it can find out whether the compressor is still working optimally or not (Hasan et al., 2009).Optimize the performance of the Propane Compressor in the Refrigeration System by lowering the suction temperature and increasing the rotation speed of the rotor.So that the compressor can work more optimally according to its operating needs (Firmansyah, 2010).
A compressor is a compressor or gas/air compressor in other words a compressor is a producer of compressed gas/air.In this industry use Positive Displacement Compressors, more precisely rotary compressor type screw compressors.This compressor compresses (adds energy) air or gas by simultaneously rotating the rotor teeth or gears that rotate in opposite directions and are interrelated (Alabdulkarem et al., 2011).These pairs of rotors rotate in unison and the direction of rotation is opposite in a fixed-height housing (casing).One of these rotors as a driver (connected directly to the driving motor) is known as a male rotor and the other as driven (driven by a male rotor) known as a female rotor whose two ends are supported by bearings.When gas enters the compressor through the suction side, it is immediately closed/blocked by a screw turn.Each gas intake is captured between the rotor gap and the casing (casing), and then the gas is transferred along the rotor groove from the inlet side to the outlet side (Giampaolo, 2010).
Page 1323 of 1327  & Tahara, 2000).e. Mechanical Seal functions to prevent leakage between the shafts that come out of the casing (shafts connected to the drive).f.Shaft is the place or position of the rotor (thread) so that the rotor can rotate.g.Slide valve Functions to adjust compressor capacity from 0% -100% or vice versa.This valve is driven by an unloader valve.The unloader valve functions to move the capacity control valve, the piston unloader moves automatically after the discharge pressure reaches ±5.9 bar, the pressure will drop to 4.4 bar, and then after ±7 seconds, the compressor will load again automatically.This valve is hydraulically driven (Hanion, 2001).
a. Balance Piston Functions to withstand axial force from the rotor (reduces load from thrust bearing).b.Lubricating Oil Hole Serves as a place for lubricating oil to enter the compressor.Lubricating oil is used to lubricate rotors, bearings, balance pistons, and unloader valves.c.Suction valve Serves to regulate the air entering the compressor.d.Outlet: Serves as an air outlet after the compression process.

a. Preparatory Stage
In the preparation stage, the author carried out several activities, including 1) Observing the environment and conditions of the research site.2) Determine the subject matter to be optimized.3) Find reference sources for writing to be evaluated.4) Determine the variable data needed for optimization.5) Field observation or process refinery overview.6) Take the necessary data for calculations (Puspawan, 2014).
b. Execution Levels At this stage of implementation, the author first conducts a literature study so that later he knows more clearly.After the author gets all the data needed for calculation, the author performs calculations using calculation parameters, volumetric efficiency, mass flow rate, and power in the compressor.By using data on inlet propane gas pressure, inlet propane gas temperature, and outgoing propane gas pressure.The results of these calculations become analytical material that will be discussed by the author based on existing theories.Until it can determine the percentage of screw compressor performance used and optimize its performance in the Refrigeration system in the Company's LPG Plant plant area X.

c. Solution Levels
At this stage, an analysis is carried out based on the results of calculations and observations that have been made at the implementation stage.After an analysis of the calculation results, the author concludes the subject matter in writing this Compulsory Working Paper and provides suggestions based on the results of the discussion with the aim of correcting the shortcomings found so that it is more optimal performance.So the output from the chiller will go to the Refrigerant Suction Scrubber, to capture the propane liquid that is included so that only dry propane vapor comes out to flow as a (first state) suction compressor.While the Economizer occurs a cooling process between propane and propane (cooling itself) and the output of propane steam will flow as a (second state) suction compressor.

RESULT AND DISCUSSION
In addition, there is oil injection as a lubricant derived from the Refrigerant Oil Cooler.The discharge gas flow will flow to the Refrigerant Separator and the oil will return to the reservoir.The specifications of oil props used are specific gravity 0.992, viscosity 64.5884 cSt, and temperature 50 ° C.
The feed used is pure propane purchased from Pertamina.Therefore, the compressor functions to maintain circulation so that the volume does not lose much.Because not every year a new propane feed injection is carried out.The composition of pure propane used C2=0.8%,C3=97.2%,C4=2% (this data is obtained from the supervisor's explanation).As for propane specification, in general, the freezing point is at temperature -47,2 °F, specific gravity 1,52, and density49 g/cm 3 .

How to Optimize
Based on the results of the performance evaluation, optimizing compressor performance using 2 approaches, namely as follows: a) Process Optimization 1) Lowering the Compressor Suction Temperature.
If the compressor inlet temperature is high, it can cause fluid with a fraction heavier than the fluid served by the compressor cannot be separated as a result of which the fluid enters the compressor which can cause dirt and vibration.In addition, if the compressor inlet temperature is high, the compressor outlet pressure will decrease.Lowering the compressor inlet temperature can be done by cleaning and repairing refrigerant suction scrubbers and economizers.The cleaning and repair are expected to make the suction ability of the Propane Compressor maximum.
2) Increase the rotational speed of the rotor.
With the increase in rotor speed, it will accelerate the suction and compression process of propane on the compressor.And can also enlarge the capacity reservoir inside the compressor.This can be done by observing and injecting lubricating oil into the compressor.b) Mechanical Optimization 1) Maintenance of Supporting Equipment and Monitoring.Maintenance of Supporting Equipment and Monitoring Propane Compressor C-440 A. Carrying out routine maintenance on supporting equipment and monitoring compressor performance can improve the reliability of the compressor itself.

Optimization Calculation
After improvements are made to the Refrigerant Suction Scrubber and Economizer is expected to reduce the temperature with relatively the same ability so that the combined temperature before entering the Propane Accumulator can be lower, which is in accordance with the capabilities of the cooler design.So after getting a lower intake temperature, it can be re-rated to determine the new capacity and flow rate.For re-rating the compressor, data with the same parameters as the actual are needed, but with lower T1 and increased N.

d. CONCLUSION
Based on observations/optimizations that have been carried out between the design data and the results of actual operation calculations with the optimized data from the current Propane Compressor, the following conclusions can be drawn.1) Propane Compressor capacity with design data of 33057.78cfm resulted in an actual calculation of 30614.40cfm and optimization of 30902.03cfm.The result of this capacity calculation has increased by 9%, which is the main concern in terms of this optimization.2) Propane Compressor Mass Flow Rate with design data of 982.7 lbm/min resulted in an actual calculation of 627.92 lbm/min and optimization of 654.80 lbm/min.The results of this calculation have increased by 4%, also a major concern in terms of this optimization.