Technology and Processing

Technology Processing

Prometheus has compiled a valuable technology portfolio of experience and intellectual property for integrated gas purification and liquefaction systems. This experience ranges from the purification and liquefaction of various methane-bearing gas streams on a small-scale to a unique method for the bulk separation of carbon dioxide (CO2) from waste gas streams. In addition to these technologies, Prometheus also has an advanced regenerative gas refrigeration cycle.

Prometheus’ Chief Technical Officer, Dr. John A. Barclay, is a globally recognized cryogenics engineering expert with more than 125 publications and 15 patents. He now leads a team of highly skilled and innovative engineers in our Advanced Development and Engineering departments. Their efforts continue to focus on the development of purification and liquefaction systems and other related technologies.

We have successfully converted both landfill gas (“LFG”) and gas from stranded wells into LNG. A pilot-scale system for conversion of LFG to LNG was successfully designed, manufactured and installed at a municipal landfill in Victoria, B.C. in November 2000. The system operated as an experimental system during most of 2001. That system successfully purified and liquefied the methane component of a complex LFG mixture into high purity LNG.

This project led to the design and manufacture of a stranded gas well-to-LNG system with a capacity of 5,000 gallons per day. This system was designed to process gas from a stranded well with various components such as nitrogen, ethane, propane, and small amounts of carbon dioxide, into LNG containing >97% methane. That system was installed at a stranded gas well outside of Sacramento and has produced over 300,000 gallons of high purity LNG.

Technical Approach

Our process utilizes filters, phase separators, selective reactions, physiadsorption, freezing and cryogenic refrigeration techniques to purify and liquefy the LFG feed stream to produce LNG that has greater than 97% methane. While the basic technologies have been successfully used commercially for many years, our unique integration has made Prometheus a recognized leader in small-scale liquefaction.

Prometheus’ process design incorporates a systematic approach to purification of LFG prior to and while cooling and liquefying the feed gas mixture. The process also uses a novel method to reject N2 from the LNG. The optimal recapture of work and thermal energy increases the overall thermal efficiency of the system while minimizing its capital costs.

Prometheus LNG systems are very flexible and have the capability to operate over a wide range of production rates around their optimum design. For example, our systems are designed to produce 10% over its nominal rating but can be turned down to produce as little as 50% of its nominal rating while operating stably. This makes our purifier/liquefier systems quite forgiving of anticipated fluctuations in feed rate or CH4/CO2/N2 concentrations. Once commissioned, our plants can be operated unattended by remote monitoring between onsite scheduled maintenance and walkthroughs.

Our Unique Technology

To produce liquid natural gas (LNG), the feedstock must be compressed, purified and cooled. To accomplish this, Prometheus uses a modular approach comprised of the integrated modules. The following is a landfill gas system, which is our most robust system given the impurities contained in the feedstock. Some skids may be unnecessary or redesigned for particular gas compositions.

  • Pre-Purification Module. The multipurpose, highly effective Pre-Purification Module removes corrosive sulfur compounds, low concentrations (parts per million) of non-methane-organic compounds (NMOCs) including siloxanes, and water from the LFG process stream and also compresses the LFG from ~2 psig to ~50 psig or more as required.
  • Bulk Purification Module. The Bulk Carbon Dioxide (CO2) Purification Module further purifies the LFG process stream by removing CO2 from the gas stream. The CO2 is removed using a proprietary cryogenic freezing technique that simultaneously pre-cools the methane (CH4) and any nitrogen (N2) while freezing out the CO2.
  • Liquefaction and Post-Purification Module. The combined Liquefaction and Post-Purification Modules liquefy the purified LFG and enhance the concentration of CH4 in the LNG by dynamic flash evaporation of the N2. The N2 rejection steps reduce the N2 concentration to less than 3% in the LNG.
  • Refrigeration Module. The Refrigeration Module provides the cooling to the process stream in the purification and liquefaction modules. The refrigeration system is a closed loop system that uses a separate refrigerant and therefore remains immune from process stream variations. Careful use of the cryogenic refrigerant allows maximum pre-cooling of the LFG process stream in stages, which is an important feature for increasing the thermodynamic efficiency of the overall purification and liquefaction.
  • Instrumentation and Controls Module. The entire LFG-to-LNG system is controlled by a distributed control system (DCS) that has inputs from all the components and process variables in the system.