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Novel Seal Design for Effective Mitigation of Methane Emissions from Reciprocating Compressors
Project Number
DE-FE0029021
Last Reviewed Dated
Goal

The goal for this project is to develop a liquid seal that demonstrates the potential for methane emissions reduction of at least 95% of 1% of the total compressor mass flow compared to the typical leakage rate of state-of-the-art dry seal packing systems. The work proposes to design, build, assemble, and operate a liquid seal. This includes the design, development, and fabrication of all components related to the seal such as the hydraulic support system. Component level commissioning will be performed in a staged order. Both static and dynamic testing of the system will be performed.

Performer

Southwest Research Institute (SwRI), San Antonio, TX 78238
NextSeal AB, Stureplan 15, SE – 11145 Stockholm

Background

Methane emissions from reciprocating compressors in the U.S. natural gas industry account for over 72.4 Bcf per year according to a 2006 statement by the United States Environmental Protection Agency. Methane has a global warming potential 50 times stronger than carbon dioxide, and reciprocating compressors are the machinery type with the highest contribution to methane emissions at natural gas transmission stations. The largest contributing factor is leakage from the sealing components in the packing systems around the piston rods.

Current technology uses a series of specifically-cut, dry-ring seals held in place with springs and cups. However, designing seals based on today’s technology inevitably leads to a trade-off between leakage reduction with minimal gaps between the seals and the rod versus allowing sufficient gaps such that the friction between the parts is sufficiently reduced allowing for movement. Once the piston moves, the pressure differential across the packing seals creates a twisting effect on the seal allowing substantial amounts of natural gas to leak into the casing. Ring twisting also causes increased friction and wear to the sealing rings and compressor rod. This gas is typically vented into the atmosphere normally exceeding 11.5 standard cubic feet per hour for new, correctly-installed packing systems on well-aligned shafts. 

This project will take the concept of liquid sealing and combines it with a novel, patented arrangement for pressure balancing across a seal arrangement (Patent No: US 7,757,599 B2) to allow for successful implementation in a dynamic environment with moving parts as shown in the figure below. The proposed seal design has been successfully implemented and tested at the bench-scale level. The seal will be designed, modeled, and fabricated for full-scale operation and tested in a reciprocating compressor system for various scenarios in a step-wise iterative method.

Impact

The primary benefit of this program is the development of a technology that will reduce and nearly eliminate methane emissions from reciprocating compressor packing. In this work, a liquid seal will be designed and tested at typical midstream pipeline operating scenarios to ensure the reduction of the environmental impact of process gas leakage from reciprocating compressor operation. 

There are significant benefits to using a liquid packing seal, some of which are:

  • Reduction of methane leakage from reciprocating compressor packing
  • Characterization of the leakage rate of typical reciprocating compressor packing
  • Longer seal life due to a reduction of differential pressure (forces) across the internal packing ring seals
Accomplishments (most recent listed first)
  • Installed and commissioned the seal and hydraulic support system with emissions measurement device in the test compressor cylinder
  • Succesfully performed dynamic and static testing of the full scale liquid packing seal in an open benchscale type test rig with zero observable process gas leakage
  • Developed a monitoring software system to measure pressures, temperatures, flow rates, displacement of the active valve, and emissions
  • Completed the hydraulic support system design, fabrication, and procurement along with commissioning
  • Completed fabrication and machining of the new liquid packing seal design
  • Developed a 1-D CFD flow model of the liquid seal pressure balancing concept—this evaluates pseudo-steady-state and dynamic conditions of the seal-piston-rod systems, taking into account the dynamics of the piston system and fluid losses through the passages and manifold
    • Performed dynamic simulations of normal and off-design events using pressure versus time data from the reciprocating cylinder
    • Calculated boundary parameters for the dimensions of the chambers containing the liquid and the active valve passageway
  • Created a solid model of the existing packing cups and ring seals as a baseline for modifications to incorporate the new seal design
  • Performed baseline testing for static compressor operation to measure leakage rates with a new standard packing for comparison with the new seal design
  • Performed baseline testing for dynamic compressor operation to measure leakage rates with a new standard packing for comparison with the new seal design
  • Ordered and installed new packing internals for the reciprocating compressor
Current Status

The novel liquid packing seal design has been fabricated and performed successfully in the intial testing. The full-scale packing seal was tested in a well instrumented benchscale type of set-up outside of the cylinder casing using process fluid from the reciprocating test compressor, operating both statically and dynamically. The test data showed the packing seal successfully pressure balanced the process gas and liquid over a range of dynamic pressures with zero observable leakage of gas into the oil lines, or oil into the gas lines. The seal has been installed in the test reciprocating compressor cylinder, and the support systems and leakage measurement devices are fully commissioned in preparation for in-cylinder static and dynamic testing.

Project Start
Project End
DOE Contribution

$797,517

Performer Contribution

$201,281

Contact Information

NETL – Joseph B. Renk III (joseph.renk@netl.doe.gov or 412-386-6406)
SwRI – Sarah Simons (sarah.simons@swri.org or 210-522-2418)

Additional Information