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Turbines for Synthesis Gas PUBLIC ACCESS

A Powerful Steam Turbine, Tailored for the Ammonia and Methanol Markets, Should Help Syngas Companies Meet Booming Future Demand.

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Mechanical Engineering 120(08), 72-73 (Aug 01, 1998) (1 page) doi:10.1115/1.1998-AUG-6

Abstract

This article reviews on one of the most demanding applications for steam turbines, which are providing the extraction steam for the production of ammonia and methanol synthesis gas, or syngas. Dresser-Rand Energy Systems, Wellsville, NY, designed their Syngas Steam Turbine specifically to meet these requirements. Demand is expected to grow for both ammonia and methanol. Ammonia is the source for most of the nitrogen fertilizer produced globally. The capacity in 1996 was 117 million metric tons, up from 113 million metric tons five years earlier. Dresser-Rand approached the syngas project with more than 30 years’ experience as a leading supplier of compression equipment for ammonia plants. The first Syngas Steam Turbine, and its complete compression train including Dresser-Rand DATUM compressors, was shipped to a methanol plant operated by Qatar Fuel Additives Ltd. in the Mesaieed Industrial Area, Qatar. It is scheduled to begin operation by the middle of next year, producing 610,000 metric tons of methanol annually. Dresser-Rand engineers have also adapted their Syngas Turbine technology for different applications.

Article

One of the most demanding applications for steam turbines is providing the extraction steam for the production of ammonia and methanol synthesis gas, or syngas. The process requires high turbine speeds (10,000 to 13,000 rpm for ammonia, 9,000 to 11,500 rpm for methanol) and high power, (typically 15,000 to 25,000 kilowatts for ammonia, and 15,000 to 30,000 kilowatts for methanol). In addition, the steam turbine's inlet steam conditions can range up to 1,800 pounds per square inch and gauge at 975° F. Dresser-Rand Energy Systems of Wellsville, N.Y., designed their Syngas Steam Turbine specifically to meet these requirements.

Demand is expected to grow for both ammonia and methanol. ammonia is the source for most of the nitrogen fertilizer produced globally. The capacity in 1996 was 117 million metric tons, up from 113 million metric tons five years earlier. J.R. LeBlanc, vice president and product director of fertilizers at Kellogg Company, Houston, estimates that by the year 2005, worldwide ammonia capacity will exceed 126 million metrictons. Chemical grade methanol is also valued as a primary building block for emissions-reducing gasoline additives, formaldehyde, and other chemical products.

Both ammonia and methanol are produced from natural gas feedstock. Although there are some refinements, depending on the feedstock and application, natural gas feedstock is heated, and then pressurized by centrifugal compressors, which causes catalytic reactions to produce the end-products. These compressors require large amounts of energy to accomplish this task; typically, half of the natural gas in an ammonia plant serves as fuel and the other half is used as feedstock. Ammonia and methanol plant operators use steam turbines as compressor drivers because of their inherent reliability, efficiency, and ability to provide high speeds and high power in a compact space.

Dresser-Rand approached the syngas project with more than 30 years' experience as a leading supplier of compression equipment for ammonia plants. "This extensive experience in compressor systems for syngas processes gave us a wealth of information to draw upon in drafting the requirements for the design of a high-efficiency steam turbine driver," said George Lucas, manager of project engineering at Dresser-Rand.

Lucas explained that his design team sought to address the challenging combination of high inlet pressure and temperature, along with the high speed and power requirements that are essential for syngas processes, while still achieving high efficiency. To that end, Dresser-Rand engineers designed a single-case, controlled-extraction turbine. The turbine is equipped with a high-pressure and temperature inlet, condensing exhaust, and double extended shaft ends to drive one or more compressors from each end.

The 50-ton turbine is compact, measuring 11 feet long, 10 feet wide, and 12 feet high. The n01Tlinal bearing span of the new turbine is 96 inches. Its inlet pressure and temperature ratings are up to 2,000 pounds per square inch," and gage at 1,000°F. The flowpath consists of a two-stage high-pressure section and a five-stage condensing section.

Engineers used a combination of blades and buckets in the flowpath design to accommodate the high-pressure and low-pressure performance of the syngas turbine. In the case of the high-pressure stages, where most of the turbine 's power is achieved, buckets are mounted in the disk using axial fir tree roots. These buckets are made of 422 stainless steel, which imparts higher strength and temperature resistance than the 403 stainless steel typically used. The syngas blades are integrally shrouded, and a trapezoidal damping wire is inserted in a groove machined in the bucket shroud to strengthen the structure.

Conversely, in the low-pressure stages, the turbine design needed to accommodate both high operating rotational speeds as well as higher flow during start-up. As a result, Dresser-Rand fashioned 2:1 aspect blade lengths made from high-strength titanium. The blades measure 3.75 inches at their base, and are 7.5 inches tall.

"The Syngas Turbine blades grew out of our evolutionary changeover from double flow designs with half height stages in all of our machines," explained Lucas, who credited Finite Element Analysis with making the improvement possible. Designers also reduced the overall length and weight of the Syngas Steam Turbine rotor by using solid-forged rotor and integral coupling flanges, thus improving rotor dynamics and facilitating their serviceability.

The first Syngas Steam Turbine, and its complete compression train including Dresser-Rand DATUM compressors, was shipped to a methanol plant operated by Qatar Fuel Additives Ltd. in the Mesaieed Industrial Area, Qatar. It is scheduled to begin operation by the middle of next year, producing 610,000 metric tons of methanol annually.

Dresser-Rand engineers have also adapted their Syngas Turbine technology for different applications. "We are using the lower pressure sections of the Syngas Turbine to drive Dresser-Rand compressors at smaller-scale ammonia plants than in Qatar. These machines operate at 12,000 kilowatts and run at 13,500 and 11,000 rpm, respectively," said Lucas.

Dresser-Rand engineers designed their Syngas Turbine to serve the demands of ammonia and methanol synthesizing.

Grahic Jump LocationDresser-Rand engineers designed their Syngas Turbine to serve the demands of ammonia and methanol synthesizing.

Copyright © 1998 by ASME
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