Project SynopsisProvide process engineering technical guidance to help develop a project for producing product quality hydrocarbons from a municipal solid waste (MSW) syngas, as well as performing process alternatives technical and economic evaluations.
CONCEPTUAL PROCESS TECHNICAL ALTERNATIVES EVALUATION OF A MSW SYNGAS SEPARATION SYSTEM
The client, a technology consulting company, contracted with Process Engineering Associates, LLC (PROCESS) for development of a preliminary process design for the conversion of municipal solid waste (MSW) via pyrolysis into hydrocarbon transportation fuels, including C3, C4, and C5+ products. The client provided a conceptual design for the process, however, many key unit operations required development. The client provided the design and technology for feed preparation and the electrically-heated pyrolysis reactor, and PROCESS was responsible for assessing and selecting the other downstream process operations. The ultimate goal was to produce a block flow diagram adequate to begin an FEL-2/3 design in the next phase.
Key contributions by PROCESS to the project included the following:
- Feedstock definition. The existing composition information on the pyrolysis gas was inadequate for design, with no information on tars or particulates, and very limited information on higher hydrocarbons and key trace impurities. PROCESS helped identify three new laboratory facilities to provide chemical analysis of the sampled pyrolysis gas, and coordinated multiple tests with the laboratories. This information was critical to subsequent process development and design work. It included the following:
- Better definition of hydrocarbon fractions and isomers through C7.
- An estimate of the tar composition and loading to provide a basis for tar removal, including definition of a simplified basis to represent an extremely complex mixture of tars (many dozens of compounds). Tars generally represent the most difficult separation for pyrolysis processes.
- Better definition of critical trace impurities, especially chlorinated compounds and sulfur. Chloromethane and chloroethane in particular were identified as difficult trace materials requiring special attention in the design.
MSW pyrolysis produces significant amounts of solid particulates that must be removed to protect downstream equipment. PROCESS worked with the client to qualify a test firm to perform an EPA Method 5 particulate sampling analysis that estimated both particulate loading and particle size distribution. This information is critical to the design of particulate removal equipment.
Based on the substantial analysis of the various test results, PROCESS prepared a feedstock definition in the design basis. While this basis cannot address all components on a definitive basis without additional work, the current basis is believed to be adequate for the next phase of work (see below).
- Product specifications. PROCESS helped the client clarify and define quality specifications on the proposed hydrocarbon products. As the feedstock definition work progressed, it became obvious that there were multiple impurities of potential concern to product off-takers. PROCESS identified these key impurities (olefins, chlorinated species, sulfur, etc.) and provided estimates of product compositions and octane values using CHEMCAD simulations of the distillation system. Discussions with off-takers by the client (assisted by PROCESS) made clear that the off-takers were not familiar enough with multiple impurities (which are not present in typical refinery or NGL feedstocks) to assess whether the products were acceptable or not. Without clear specifications on products, it became clear that a robust design of the hydrocarbon purification systems was not practical at this time. This led to the decision to change the nature of the project (see below).
- Three major subsystems were identified as necessary and PROCESS took the lead in assisting the client in identifying and/or managing suppliers for these subsystems:
- Tar removal: Tar removal has long been regarded as the most difficult unit operation in converting pyrolysis gas into useful products. PROCESS surveyed the available technology, and identified a provider in Europe as the best potential supplier due to their extensive experience. PROCESS wrote a design basis and preliminary RFQ for the company, and coordinated the technical evaluation of their offering. It has been decided to use this European company for the next phase.
- Hydrocarbon condensation and separation: Prior to PROCESS’ involvement, the client had identified a technology company as a promising candidate for the recovery and separation of the valuable hydrocarbons from the substantial amount of light gases (H2, CO, CO2, C1-C2, etc.) present in the pyrolysis gas. The initial feedstock definition to this technology provider was inadequate, and PROCESS worked diligently with the client and the technology provider to improve the design basis for their system. PROCESS provided an updated design basis to the technology provider for their design, and defined which impurities the technology provider could and could not address (e.g., the technology provider was unable to remove chloroethane and sulfur). PROCESS reviewed the technology provider’s designs.
- BTEX removal: Feedstock definition showed that substantial amounts of olefins and aromatics were present in the pyrolysis gas. It was very likely that the levels of aromatics (BTEX: benzene, toluene, ethylbenzenes, and xylenes) were unacceptable in the hydrocarbon products. PROCESS identified a smaller systems supplier to provide a design for BTEX removal; it became clear that larger suppliers were not interested in a very small, specialty BTEX removal system. This smaller technology provider supplied a design for an extractive distillation system that was reviewed and accepted by PROCESS as a preliminary design solution to this difficult separation.
Following the work above, it became clear that the design basis remained inadequate to proceed with the hydrocarbon production plant, due largely to the lack of definition on clear specifications on products, especially on trace impurities. PROCESS proposed that in the near-term the pyrolysis gas could be converted into electric power using a boiler/steam turbine system. A block flow diagram for the power generation project was prepared, and initial estimates of power were made. The proposal for a power generation facility plus a pilot plant were accepted by the board for the facility, and the client is progressing to the next phase of development with PROCESS as the process engineering company.
- Alternative Fuels Production / Landfill Alternative Energy Production
- Process definition
- Complex design basis preparation
- Process alternatives technical and economic evaluations
- Process technology provider evaluation identification and technical management
- Owner’s engineer technical support.