Natural Gas Liquid (NGL) processing plants are important energy consumers in Saudi Aramco. It consumes both thermal energy in gas treating (water, CO2 and sulfur removal) and mechanical energy in gas processing to produce sales gas and NGL.
In this part of the manual gas processing facilities’ components are approached from energy consumption point of view, followed by typical gas processing plant description and concluded with major energy conservation guidelines.
Energy Efficiency in Gas Processing Plant
Energy Usage Analysis
This part is intended to allow the reader to account for and to analyze the efficiency of energy usage in gas processing. Energy usage can be made directly translated into costs and, in many cases, gas or oil reserves. Therefore, it is imperative that all energy be utilized at efficiencies resulting in maximum long range profit. The accounting analysis will ensure that all BTUs purchased or directed from production for use within the operation are traced and balanced against usage. The efficiency analysis shall determine the actual and theoretical efficiency of individual pieces of equipment and the average efficiency of all equipment within any plant.
This part will analyze the energy being consumed and give direction where the existing equipment is inefficient.
Although vigilance for any possible improvement in gas processing plants’ integration is always important, the scope of this part is limited to efficiencies of energy usage within the operation and simple example for heat integration in a gas processing plant’ liquid recovery unit.
Energy Accounting Analysis
In order to make the type of energy usage analysis dictated by the cost of energy and the character of our business today, it is mandatory that we start with full identification and accounting of all energy that is purchased or directed from production to usage within the geographical confines of the operation being studied. To do this the total BTUs obtained from each principal metering point must be balanced against the sum of the BTUs obtained from measurements made at each usage point. After this is done, energy losses can be located, eliminated and each usage point analyzed for efficiency.
Energy Efficiency Analysis
Basically the efficiency analysis is a comparison of the actual energy consumed versus the theoretical work input into the fluid. The work input into fluid will be either in moving the fluid (mechanical energy) or in changing the temperature of the fluid (thermal energy). The ratio will always be less than one. All equipment has inherent inefficiencies; for example fraction or less than 100% combustion.
Optimum Fuel Consumption of Existing Equipment
To determine how efficiently the existing equipment in a field is operating, the actual fuel consumption of each piece of equipment can be compared to its optimal fuel consumption. Most manufacturers will provide fuel consumption data or fuel consumption curves for their equipment. When calculating optimum fuel consumption the operating conditions such as temperature, pressure, volume etc. must be considered.
After the optimum fuel consumption is calculated, it can be compared to the actual fuel consumption. If the optimum consumption is thought to be a reasonable number and it compares closely with the actual consumption, the equipment may be operating at its peak efficiency. If the two numbers are not close, the reasons for the excessive fuel consumption should be investigated.
In some instances, a process change may increase the efficiency of a field operating without requiring additional investment. A good example of this in Amine Gas Sweetening Plants is to increase the amine percentage of MEA to at least 15%. Another consideration would be to change from MEA solvent to UCARSOL HS Solvent 101. This solvent can be utilized in a 50% solution instead of 15 – 20% for MEA.
Best Available Technology
In many instances even if the equipment in the field is operating at its optimum efficiency, the energy consumption is determined to be excessive when compared to new more efficient models. If this is the case consideration should be given to replacing with the more efficient models. The common replacement has been to replace gas driven or engine driven pumps with electric motors.
To determine what is the least amount of energy that need be consumed to do a specific job the energy consumption of the most efficient unit possible for the job must be calculated. In other words, energy consumption using “best available technology” must be calculated and compared to the actual. This will show what savings can be possible using the most efficient equipment available.
Of course, in a large amount of cases it is not economically feasible to replace equipment for the sole purpose of energy saving. However, when installing new equipment or replacing defective equipment, energy consumption should be a major consideration.