This article focuses on synthetic gases derived from industrial and municipal wastes enable fuel cogeneration plants in Europe. The modern version of the fabled philosopher’s stone is gasification, a process typically used to convert high sulfur coals into a synthesis gas, or syngas that can be burned cleanly. Basically, the coal is prepared and fed into a reactor, or gasifier, where it is partly oxidized with steam under pressure. GE has developed co-firing capability that allows the power plant to produce full electrical load on the backup fuel, providing electric power availability up to 95%. Waste-fueled IGCC plants are being built in countries other than Italy and Germany. Asian petrochemical plants are also bullish on waste-fueled IGCC. GE is working with Exxon in Singapore to gasify the residues from steam cracking operations at a major olefins plant in the island nation. In addition to providing power and steam, gasification will produce all the hydrogen feedstock the plant needs for olefin processing when it begins operations.
Alchemist in medieval Europe sought the philosophers stone that they believed would enable them to transform lead into gold. Today, their descendants in Italy and Germany are converting the carbon in oil-refining tar, plastic wastes, and steel-furnace gas into a synthesis gas that provides electricity, process steam, and valuable chemical feedstock.
The modern version of the fabled philosophers stone is gasification, a process typically used to convert high sulfur coals into a synthesis gas, or syngas, that can be burned cleanly. Basically, the coal is prepared and fed into a reactor, or gasifier, where it is partly oxidized with steam under pressure. By simultaneously reducing the presence of oxygen in the gasifier, the carbon in the coal is converted into a gas that is 85 percent carbon monoxide and hydrogen, with smaller portions of carbon dioxide and methane.
Sulfur is removed from the gasified coal and is sold in its elemental form, or as sulfuric acid. Inorganic materials such as ash and metals drop out as slag, which is typically used for construction materials.
When coal is gasified to generate electricity, it is typically consumed in an integrated gasification combined cycle, or IGCC, configuration, to improve the energy efficiency of gasification plants, which are inherently more expensive than conventional coal-fired power plants. In the combined cycle, gas is burned in turbines to produce electricity, and exhaust is recovered to produce steam in a boiler that powers another turbine to generate additional electricity. The plant may provide process or heating steam as well.
The integrated gasification combined cycle process was originally designed to convert high sulfur coal into more environmentally benign synthetic gas.
While mechanical engineers work to make IGCC plants more economical, they tout the environmental advantages of burning syngas, a cleaner-burning fuel than coal. The same ecological benefits underpin the Italian and German plants, which convert waste materials containing carbon into gas turbine fuel.
All of these plants rely on heavy-duty gas turbines that the General Electric Co. in Schenectady, N.Y., has been modifying for IGCC service since 1984, when the first IGCC plant, the Cool Water Demonstration Project in the Mojave Desert in California, came online.
Weve accumulated 320,000 hours of syngas-fueled power generation worldwide since Cool Water, said Douglas Todd, a chemical engineer and manager of process power plants at GE. We joined Cool Water to demonstrate how the advantages of combined cycle costs could be applied to fuels other than natural gas. We believe that 30 percent of the worlds power plants to be built in the next 10 years will be designed to consume coal or oil. IGCC can make them cleaner and lower the costs of the electricity they produce.
Other economics are spurring the development of waste-fueled IGCC plants. When we built Cool Water, the IGCC technology generated electricity at a cost of $2,000 per kilowatt. Since then, we have got the cost of IGCC-generated electricity down to less than $1,000 per kilowatt. Using waste fuels helps to reduce the cost of electricity even further, explained Todd.
This is particularly true for the wastes generated by oil refining, such as petroleum coke. Most of GEs orders for IGCC turbines are for petroleum coke plants, most recently, under construction in France, Spain, and the United States, Todd said. For example, the Delaware Star refinery in Delaware City, Del., was recently converted to gasify solid-waste petroleum coke to power four GE 6FA gas turbines.
General Electrics experience is underscored by the first World Gasification Survey conducted by SFA Pacific Inc. of Mountain View, Calif., in 1999. This survey was supported by the U.S. Department of Energy and member companies of the Gasification Technologies Council in Arlington, Va. The survey identified 160 commercial gasification plants operating, being built, or planned in 28 countries around the world.
The survey showed that in the 1990s, gasification capacity fueled by petroleum-based materials, including residual oil, petroleum coke, and tars, was approximately 60 percent of coal-fueled capacity. However, the survey found that refining industry economics, stricter environmental regulations, and electricity deregulation that enable oil refineries to generate power and compete in open energy markets would increase the use of petroleum material gasification. The study forecast that after the current year, petroleum-based gasification capacity would grow almost twice as fast as coal-based gasification capacity.
Turning Tar Into Sardinian Power
The surveys findings are supported in the worlds largest IGCC power plant, recently constructed by a consortium including Snamprogetti S.p.A. of Milan and GE Power Systems of Schenectady on the Italian island of Sardinia. The IGCC plant is located at the Saras Oil Refinery in Sarroch, the second largest European refinery. The plant has been running on syngas since August, and produces 551 megawatts of electricity, 285 metric tons of process steam for the refinery, as well as 20 million standard cubic feet a day of hydrogen feedstock. The Sardinian facility is owned by Sarlux S.r.l., a joint venture formed by Saras Raffienerie S.p.A. of Milan and Enron Corp. of Houston.
The Sarlux IGCC plant gasifies the tar-like residue produced by vacuum visbreaking at the Sarroch refinery. Vacuum visbreaking is a form of thermal cracking of petroleum that dates back to the 1930s. Visbreaking involves subjecting heavy crude oil to pressure and heat to physically break its large molecules into smaller ones to produce lighter fuels, such as gasoline and diesel fuel.
Originally, the visbreaking tar at Sarlux was incinerated in boilers to make electricity for ENEL, the national Italian power company. By 1990, environmental regulations prohibited the practice. IGCC was already an ecologically viable alternative, so GE and its Italian partners worked to get the laws revised to allow refining companies to sell power, and assisted legislation that would set a competitive price for electricity generated by waste- derived fuels.
The visbreaking tar is a thick liquid that is pumped to the gasifier unit, which is licensed from Texaco Inc. in White Plains, N.Y., and was originally used in the Cool Water program.
Oxygen is added to the gasifier to partly oxidize the tar under pressure. This causes the carbon and the oil in the tar to change to carbon monoxide rather than carbon dioxide, and the hydrogen present to become gaseous hydrogen, rather than water. The plant then separates the elementally pure hydrogen that Sarlux uses to upgrade all its finished fuel products, such as gasoline. The remaining syngas is sent to the turbines to make power.
There are three GE 109E, single-shaft combined cycle systems built by GE and its subsidiary, Nuovo Pignone of Florence. Each GE STAG (steam and gas) system consists of a GE MS9001E gas turbine, a GE 109E condensing steam turbine, a double-end generator, and a heat recovery steam generator.
The turbines are started up by distillate oil, are injected with steam to control nitrogen oxide formation, then are switched over to syngas. Distillate oil also serves as the backup fuel for the Sarlux turbines.
We designed the turbines to handle syngas with 40 percent moisture, and a heating value one-sixth that of natural gas. The combustor design has to handle six times the amount of syngas compared to natural gas. This means the fuel delivery system must deliver the higher volume and be explosion-proof, due to the hydrogen fuel, said Todd, who added that these proprietary modifications grew out of GEs Cool Water experience.
Each Sarlux turbine produces up to 186 MW of electricity while meeting Italian emission levels of 30 parts per million for nitrogen oxides and sulfur oxides. GE adds the 40 percent moisture to the fuel to reduce NOMx formation. Noise levels must be less than 85 decibels at the equipment.
The Sarlux IGCC plant will generate about four billion kilowatt-hours of electricity annually that will be sold to ENEL. This energy will be distributed throughout Sardinias electrical grid. Sarlux will also generate fresh water.
We Gasify Anything
In Spreewitz, Germany, north of Dresden, Sekundar-rohstoff-Verwertungszentrum Schwarze Pumpe GmbH operates an IGCC facility that converts an eclectic mix of 450,000 metric tons of solid waste, and 50,000 metric tons of liquid wastes, into electricity, steam, and methanol feedstock. SVZ was founded in 1995 as an independent subsidiary of Berlinwasser Holdings to operate the Spree witz plant, which was originally designed to gasify brown coal in the 1960s. The company has spent more than $250 million so far in an ongoing effort to modernize the plant to gasify a wider variety of solid and liquid wastes.
The solid materials treated at Spreewitz include plastic wastes, wood from junked railroad ties and telephone poles, sewage sludge, old tires, and household garbage. These materials are ground up, pelletized, mixed with coal, and sent into four solid-bed gasifiers made by a variety of manufacturers. The reactors process up to 15 metric tons of waste hourly.
Steam and oxygen are injected into the reactors, which are internally pressurized to 25 bar, and heated to 800 to 1,800°C, depending on the type of gasifier. The syngas that is generated is drawn off into a vessel where water cools the raw gas before it is sent to the combined cycle power plant or the methanol plant. Solid residues, basically ash, from the gasification process drop into the quenching zone of the reactor and form slag. A rotating grate at the bottom of the quench removes the slag.
Up to 200 tons per day of liquid wastes, primarily spent oils, tars, slurries, and oil-water emulsions, are sent to two Endrainet flow gasifiers at the Schwarze Pumpe facility. The Brenstoff Institut in Frieberg, Germany, originally developed the Endrainet gasifier.
Steam drives the liquid wastes over a natural gas-fired burner system in each Endrainet reactor that raises the temperature within the reactor to the 1,600 to 1,800°C range. These high temperatures produce syngas and destroy any organic pollutants present. The hot syngas is shock-cooled in a water quencher and drawn off for use. Quenching also prevents undesired chemical reactions and locks heavy metals into vitrified slag form.
The SVZ combined-cycle plant is built around an MS6001B gas turbine provided by Thomassen under license from GE. These turbines were adapted to burn syngas like the ones being used at the Sarlux plant.
The SVZ gas turbine produces 44.5 MW of electricity that is sold to the local grid. The MS6001B exhaust is captured by a heat recovery steam generator to produce steam that is sent to a turbine purchased from ABB Turbinen in Nuremberg. The unit produces an additional 30 MW of electricity and 240 metric tons per hour of process steam for the waste treatment plant. The gas turbine also burns purge gas from the methanol plant, and uses distillate oil as its backup and startup fuel.
By late August 2000, the SVZ turbine had accumulated more than 24,000 hours of operation burning syngas.
Schwarze Pumpe produces about 100,000 tons of liquid methanol annually. SVZ adds water to the syngas to maintain a carbon-to-hydrogen ratio of 2 to 1. Then, the syngas is reacted by a catalytic process to produce crude methanol that SVZ refines until it is pure enough to be sold. Among the applications for the methanol produced at Schwarze Pumpe are gasoline additives, methylating agents in paint, ethanoic acid in wood preservatives and disinfectants, refrigerants for cooling systems, and solvents for resins and waxes.
In late September, SVZ completed construction of another gasification line at the Schwarze Pumpe plant, based on a British Gas-Lurgi gasifier. The BGL gasifier uses oxygen as a gasifying agent, improving the quality of its methanol compared to the air-blown gasifiers used originally at Schwarze Pumpe.
SVZ will send 30 tons of mixed solid waste and coal per hour into the double airlock of the BGL gasifier. Steam and oxygen are injected into the gasifier, heating the mixture to 1,600°C while pressurizing it to 25 bar. Syngas is drawn off, while molten solid residues are shock- cooled by quench to form a vitrified, granular slag for later disposal.
Berlinwasser Holdings recently agreed to sell SVZ to Global Energy Inc. of Cincinnati. The Ohio company sponsors the development of gasification technology, and has more than 4,000 MW of projects in development, under construction, or in operation in Europe and the Americas.
Furnace Gas Fuels Taranto
Steel mills can be reconfigured as sources of waste-fueled syngas because they already produce hydrocarbon gases from their furnaces and coke ovens that can be burned as turbine fuel after some solid and liquid contaminants are removed. This is being done at the Ilva Sistemi Energia cogeneration project, which uses process gases generated at the Ilva steelworks in Taranto, Italy, to fuel turbines and produce 520 MW of electricity for ENEL, and 150 metric tons per hour of process steam.
The Taranto plant is the buckle on Italys steel belt, producing nine million tons of steel plates and pipes. The plant previously relied on two conventional coal-fired steam plants to meet its steam and electrical requirements, but their combined electrical efficiency was less than 37 percent. Among the changes Ilva management instituted to raise the Taranto plants efficiency was building a power station, called the CET3, to recover furnace gases to fuel three combined cycle units to produce steam and electricity.
The CET3 power plant at Ilva/Taranto was built by a joint venture, including Ansaldo, based in Genoa, and GE-Nuovo Pignone, headquartered in Florence. The power plant is fed with blast furnace gas, oxygen steel-furnace gas (also known as converter gas), and coke oven gas. All three hydrocarbon gases are chemically similar to syngas, but the blast furnace and converter gas streams are laden with dust, and the coke oven stream is laden with liquid hydrocarbons, which require the gas streams to be treated.
The two furnace gas streams are directed through two electrostatic precipitators that remove the dust particles. The coke-oven gas is sent through three electrostatic precipitators that will remove tar particles. The gas streams are then mixed and sent through a final electrostatic precipitator before being used as fuel.
Each combined cycle unit is built around an MS9001E gas turbine manufactured by Nuovo Pignone, with each turbine capable of generating 140 MW. These turbines were modified to burn low calorific value gases, such as furnace recovery gases supplemented by natural gas, by using the GEs syngas combustion system.
The 9Es at Taranto are single-shaft machines that burn the syngas to simultaneously drive a generator and a fuel gas centrifugal compressor to pressurize the recovery gases. Each turbine is linked to a horizontal waste heat boiler that produces steam at two pressure levels, 95 and 25 bar. The boiler reheats the low-pressure steam before routing it back into a steam turbine that operates a second electrical generator that has an output of 68 MW. The high-pressure stream is used as process steam.
Both the gas turbines and waste heat boilers at CET3 can burn natural gas, recovery gas, or a mixture of both to provide fuel flexibility. The net electrical efficiency of CET3, including the power absorbed by the gas compressor and the steam cogenerated, ranges from 41.5 to 42 percent.
An additional benefit of IGCC power plants is their ability to stay online due to their fuel flexibility. GE has developed co-firing capability that allows the power plant to produce full electrical load on the backup fuel, providing electric power availability up to 95 percent. According to Todd, this has helped make IGCC more acceptable in its early developmental stages.
Todd noted that waste-fueled IGCC plants are being built in countries other than Italy and Germany. Asian petrochemical plants are also bullish on waste-fueled IGCC. GE is working with Exxon in Singapore to gasify the residues from steam cracking operations at a major olefins plant in the island nation. In addition to providing power and steam, gasification will produce all the hydrogen feedstock the plant needs for olefin processing when it begins operating later this year.