The primary 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. A secondary goal is to develop and validate a leakage model for existing reciprocating compressor packing leakage.

Southwest Research Institute (SwRI), San Antonio, TX 78238
NextSeal AB, Stureplan 15, SE-11145 Stockholm, Sweden
Williams Gas Pipeline, Houston, TX 77056

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 ^[1]. 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 ^[1]. The largest contributing factor to emissions 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) and 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 ^[2].

This project will take the concept of liquid sealing and combine it with a novel, patented arrangement for pressure balancing across a seal arrangement (Patent No: US 7,757,599 B2 ^[3]) to allow for successful implementation in a dynamic environment with moving parts. 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.

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 the development and implementation of 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 (force) across the internal packing ring seals

• Identified several packing leakage models and industry guidelines for packing leakage and performed initial comparisons of leakage predictions with JGA/2 data.
• Completed test planning and piping/bottle system design for leakage testing on an Ariel JGT/4 compressor.
• Performed baseline leakage testing for conventional packing rings on an Ariel JGA/2 compressor with high- and low-pressure cylinders under both static and dynamic conditions.
• Successfully completed dynamic testing of the NextSeal packing seal in the high pressure test compressor cylinder operating over a range of speed from 300 rpm–1,300 rpm at pressures up to 1,200 psia.
  • No gas leakage was observed using a Coriolis meter to measure gas entrainment in the packing oil drain line in combination with a rotameter on the packing vent lines.
• Successfully completed low-pressure testing of the packing seal installed in the test compressor cylinder operating dynamically over a speed range of 300 rpm–1,300 rpm up to 200 psia.
  • No gas leakage was observed using a Coriolis meter to measure gas entrainment in the packing oil drain line in combination with a rotameter on the packing vent lines
• Performed extended life testing while in static hold and found minimal wear to the seal parts
• Quantified the oil flow rate required for successful sealing in static hold
• Completed static hold testing of the packing seal in the test compressor with zero observable leakage using a Coriolis meter for gas entrainment in the packing oil drain line
• Installed and commissioned the packing seal, instrumentation and monitoring system, 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 computational fluid dynamics 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

The novel liquid packing seal design has been designed, fabricated, and validated successfully in static and dynamic performance testing in low-pressure and high-pressure cylinders at speeds of 300-1,300 rpm and pressures up to 1,200 psia. No gas leakage was detected into the packing vent, distance piece, or oil stream by various flowmeters or gas bubble visualization while operating at these conditions. Additionally, no oil leakage into the cylinder was measured during testing. With these results, project work related to the novel packing seal has concluded and current project efforts are focused on development and validation of a leakage model for existing packing. Leakage data was obtained from low-pressure and high-pressure cylinders on a JGA/2 compressor, and a JGT/4 compressor is being prepared and commissioned for additional leakage data. In addition, both a literature review identifying several existing leakage models and guidelines from the industry have been obtained and compared with JGA/2 leakage data obtained over a range of conditions to identify focus areas for model improvement.  

$1,157,517

$291,281

NETL – Joseph B. Renk III (joseph.renk@netl.doe.gov or 412-386-6406)
SwRI – Tim Allison, Ph.D. (tim.allison@swri.org or 210-522-3561)

Final Report (June 2020)
   OSTI Identifier: 1635601
 

References

1. US EPA, "Reducing Methane Emissions From Compressor Rod Packing Systems ", US Environmental Protection Agency, Ed., ed. , 2006.
2. R. K. Pachauri, M. Allen, V. Barros, J. Broome, W. Cramer, R. Christ, et al., "Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change," 2014.
3. B. Adolfsson, "Sealing Arrangement for Relatively Movable Parts and Device Including such a Sealing Arrangement," United States Patent, Jul. 20, 2010, 2006.