TECHNOLOGY Upgraded gas plant anchors reconfigured gathering system

Feb. 26, 1996
Warren R. True Pipeline/Gas Processing Editor Modifications at GPM Gas Corp.'s Linam Ranch gas plant, near Hobbs, N.M., were completed late last year, and the plant has been restarted. The company bought the plant from an Enron Corp. subsidiary at the end of 1994 (when it was processing 95 MMcfd), renamed it, and immediately set about modernizing it to improve operations and reap higher NGL recovery and increased reliability. After modifications, capacity is 150 MMcfd. With the addition of
Warren R.
True Pipeline/Gas Processing Editor

Modifications at GPM Gas Corp.'s Linam Ranch gas plant, near Hobbs, N.M., were completed late last year, and the plant has been restarted.

The company bought the plant from an Enron Corp. subsidiary at the end of 1994 (when it was processing 95 MMcfd), renamed it, and immediately set about modernizing it to improve operations and reap higher NGL recovery and increased reliability.

After modifications, capacity is 150 MMcfd. With the addition of another residue-gas-turbine compressor, capacity can be 200 MMcfd.

GPM also modified adjoining facilities better to integrate Linam Ranch into the company's reconfigured New Mexico operations (Fig. 1 [53314 bytes]).

New cryo plant

The Linam Ranch plant, formerly Hobbs Processing Co.'s Hobbs plant, has been converted from a propane refrigerated lean-oil absorption plant to a cryogenic operation, modern turbine compression has been installed, and the plant's sulfur-recovery unit has been upgraded (Fig. 2 [77596 bytes]).

The goal, according to GPM, was to achieve higher NGL recovery and install flexibility to take or reject ethane, depending on market prospects.

Current inlet-gas composition (each in mole %) is as follows: nitrogen, 2.15%; carbon dioxide, 1.55%; hydrogen sulfide, 0.61%; methane, 75.66%; ethane, 9.1%; propane, 4.99%; butanes, 2.39%; pentanes, 1.14%; and hexanes and heavier, 2.41%.

Dehydration of feed gas had been via a four-bed mole sieve unit capable of handling 200 MMcfd. This system was modified to a three-bed design with automated bed switching capable of handling 150 MMcfd of new inlet gas.

Installation of the 123.5 ft, 66-ton demethanizer column progresses as GPM carries out in 1995 an extensive upgrade to its Linam Ranch gas plant outside Hobbs, N.M.

This part of the project was started up in December 1995.

In August of last year, the company completed an upgrade of the inlet treating's control system with a Foxboro I/A DCS system.

Completed earlier in 1995 was the first phase of what the company calls its vapor-gas project.

Inlet liquids were coming into the plant at 200 psig and were lowered to 0 psig, a change that naturally created vapors. Hobbs Processing had flared these.

GPM connected the vent line, that previously ran to the flare, to a nearby gathering line to recycle any vapors. In the course of this modification, the company reduced the pressure from 200 psig to 30 psig, the operating pressure of the gathering system.

The amount of vapor sent to flare was thereby greatly reduced, and the plant's MMBTU efficiency was in creased. GPM will eventually install a stabilizer to collect remaining vapors still being sent to flare and further increase plant efficiency.

Compression; enhanced extraction

Compression at the plant has been significantly upgraded.

Inlet compression was modified by the idling of one of four HRA 1,200-hp Clark compressors and adding a Solar Taurus 70 (8,900 hp). Two TLA 2,200-hp Clarks and three HRA Clarks remain in service.

Suction pressure remained at 235 psig, discharge pressure decreased slightly to 640 psig; but inlet capacity increased to 200 MMcfd.

Residue compression was also added; none had been in place at the time of the purchase in late 1994. Installation included a Taurus 70 Solar turbine (8,900 hp) and a T-4700 Solar turbine (4,700 hp) with combined capacity of 111 MMcfd.

Residue gas leaving the new cryo plant consists of nitrogen (3 mole %), methane (96 mole %), and ethane (1 mole %). GPM says this stream will be richer if the plant is rejecting ethane.

Compression for propane refrigeration was also modified. A single Solar T-4500/York compressor (3,379 site-rated hp) with a circulation rate of 25.4 MMcfd replaced three 1,600-hp GMVh-8 Cooper Bessemer compressors.

Formerly, NGL extraction by lean-oil absorption had carried a rated capacity of 200 MMcfd. This plant was shut down and replaced with a high ethane-extraction turboexpander plant with a design capacity of 150 MMcfd and an off-design capacity of 200 MMcfd. Design ethane retention is 91%.

A Foxboro I/A DCS control system was also installed. Design NGL production is 14,750 b/d. Produced NGL will consist of the following (each in mole %): C2, 42.12; C3; 28.25; C4, 15.59; and C5+, 14.04.

For sulfur recovery, a fourth Claus bed was added to the existing three-bed Claus unit. And instrumentation was upgraded to a Foxboro I/A DCS system. Sulfur-recovery efficiency improved to 95.8% from 90%. Productive capacity became 48 short tons/day.

The overall upgrade reduced emissions from the plant by 462 tons/year of NOx, 83 tons/year CO, 2,977 tons/year of SO2, and 5 tons/year volatile organic compounds.

System reconfiguration

Purchase and upgrade of the plant at Hobbs has led GPM to reconfigure much of the gathering behind the Linam Ranch plant to focus the southeast New Mexico system on the plant's capabilities.

Acquired with the plant were 65 miles of 12 in., 1,000 psig (maximum allowable operating pressure) pipeline in Eddy County, 6 miles of 16 in., 11 miles of 24 in., and 6 miles of 24-in. pipeline (MAOP = 550 psig) in Lea County, 12 miles of 10 in. (1,000 psig MAOP), and 665 miles of 4-16 in. low pressure lines.

One result of this reconfiguration is that GPM, in first quarter 1996, is shutting down its Zia plant in far Lea County. This 29-MMcfd plant, noteworthy for being automated and remotely controlled, was dedicated in late 1993 (OGJ, Dec. 27, 1993, p. 35). It was expanded to 40 MMcfd in 1994 (OGJ, June 20, 1994, p. 29).

Volumes of as much as 32 MMcfd are being routed to Linam Ranch in a project that has required five pipeline tie-overs and installation of 3,000 ft of 10-in. pipe.

And as part of the overall project, GPM has integrated the Lea County pipeline into its Eunice system. This allowed shutdown of 22 obsolete reciprocating compressors and installation of two T-4700 Solar turbines.

Shut down were five RA8 775-hp Clarks, five HR8 851-hp Clarks, ten BA6 1,132 hp Clarks, and two TRA6 967 hp Clarks.

Emissions were reduced as a result of this part of the project by: NOx, 1,448 tons/year; CO, 274 tons/year; and VOC, 45 tons/year. There were no reductions in sulfur dioxide.

Holloman Construction, Odessa, served as both engineering and construction contractor for this part of the overall project.

Additionally, in October 1995, GPM Gas started up a bi-directional pipeline between the Eunice and the Linam Ranch plants by converting 10 miles of 16-in. gathering line to this service. This line has an MAOP of 550 psig.

Finally, GPM Gas is upgrading metering at producer sites with more than 200 electronic-flow meters (EFM).

Who was involved

Main engineering firms involved in the project were Ortloff Engineers Ltd., Midland, Tex., for sulfur-recovery unit redesign; KTI Fish Engineering & Construction, Houston, for cryogenic plant design; Merrick Engineers, Denver, for safety upgrade design, and Vertex Industrial Projects, Houston, for automation design.

Construction contractors were Fish Engineering & Construction, Houston, for SRU and cryogenic plant; and Kelley-Coppedge Inc., Fort Worth, for the safety upgrade.

Major equipment suppliers were Solar Turbines, Foxboro Controls, Ametek Analysers for the sulfur plant analyzers, Applied Automation for the on-line chromatographs, Dickson Tryer for the SRU skid, Area Tank for the carbon steel vessels, Word Industries, Oklahoma City, for prefabricated pipe, Mafi Trench Corp., San Diego, for the expander, and Vulcan Boiler Works, Sand Springs, Okla., for waste-heat recovery system.

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