(386f) Critical Approach during Design Leads to Process Design Optimization and Reduce Project Cost


In the current oil and gas market condition companies are thinking twice to install new facilities and even necessary upgrades. It is highly recommended to go only for the critical, high rate of return and cost effective projects. It is the responsibility of the engineering contractor to see the cost reduction options in the engineering design phase to help the client to make necessary decisions on budget allocation and approval.

In every NGL (Natural Gas Liquids) ethane, propane, butane, pentane etc. transportation facility, (PCP) Product Chiller Package is installed to sub-cool the NGLâ??s to compensate in advance for the heat gain in loading and recirculation lines. The sub-cooling guarantees the NGL product temperature specifications for ship loading (contractual requirement) Table-1 & 2. The loading system includes storage tanks, booster and loading pumps, chiller packages include loading and recirculation chiller package, loading pipeline and recirculation pipeline and offshore loading arms. To keep the NGL product sub-cooled and ready for ship loading it is continuously recirculated through the system, recirculation pipeline is provided from loading area back to the storage facility with recirculation chiller installed just before the storage tank.

A case study is performed to upgrade the existing Product Loading Facility (PLF) in order to enhance the operational reliability, standard requirements and to meet the product specification. The followings were the primary objectives of the case study.

1. The existing compressors of the PCP refrigeration system do not comply with API 617 (Axial and Centrifugal Compressors and Expander compressors) 8th edition as these compressors were primarily designed for industrial chilling units and then reused as refrigerant compressors of the PLF refrigeration system.

2. Freon R-22 refrigerant is chlorodifluoromethane also known as hydrochlorofluorocarbon (HCFC). It is commonly used as a propellant and refrigerant. Although Freon R-22 refrigerant has less potential of ozone depletion however Environmental Protection Agencies of different countries including US, Austraila, Canada and Saudi Arabia have planned to completely phase out its industrial use.In order to comply with government regulations, the second objective is to replace Freon R-22 refrigerant with R-507 refrigerant. R-507 is a mixture of hydrofluorocarbon refrigerants HFC-125 and HFC-143a. It is an azeotrope, nonflammable, and has no ozone depletion potential.

3. Based on evaluations, retrofitting the existing PCP is not technically feasible by replacing only the existing compressors with new compressors if Freon R-22 refrigerant would be replaced with R-507 refrigerant. This is because the process of each existing chilling unit was designed originally for Freon R-22 refrigerant. Using R-507 refrigerant necessitates new process design conditions which will require the entire replacement of vessels and equipment associated within these chilling units, including the replacement of the interconnecting piping system. So the third objective is to replace the existing PCP.

Besides the primary objective of Chillers Design for R-507 refrigerant service, the whole PLF is studied to capture any opportunity of optimization in the existing process design. The system is simulated in Aspen HYSYS from storage tanks to loading arms for worst case scenarios (i.e. max. summer ambient temperature, max. product loading flow rate etc.). After detailed analysis of the PLF following objectives selected for further detailed evaluation.

  1. Reduce heat losses in the loading / recirculation pipelines
  2. To Reduce CP heat load

Process Simulation is developed to perform the study.

Consequently, based on simulation results few modifications proposed in the existing design, with exclusion of one chiller package. By doing so one chiller package will be reduced and only three chiller packages in total will be required to meet the design objectives. The major modification in the system is to change TCV to FCV, so that flow can be adjusted on manual mode as per the loading requirement and in normal and maximum loading scenario it can provide flow equal to 2 chiller packages.