Three of five planned independent power projects using a technology that cleanly burns fluid petroleum coke have started up in the San Francisco Bay area.
Process designer Combustion Power Co. (CPC), Menlo Park, Calif., said the technology holds great promise for cogeneration and independent power projects in areas with air quality problems.
At the same time, widespread application of the technology could boost U.S. consumption of refinery petroleum coke, an underutilized, low cost product that is mostly exported from the U.S., CPC said.
The five plants, each rated to a nominal 20,000 kw, are the first commercial independent power plants in the U.S. fueled 100% by petroleum coke, CPC said. Financing of $370 million for the plants was the second biggest independent power plant financing in 1989, the company said.
BAY AREA PLANTS
CPC affiliate GWF Power Systems Co. Inc, Walnut Creek, Calif., owns and operates the five Contra Costa County, Calif., independent power plants that will produce a combined 98,500 kw of power.
Of that, net electricity produced for sale to Pacific Gas & Electric Co. will total about 89,000 kw.
The five are within a 7 mile radius of one another. They burn petroleum coke that's supplied by Exxon Corp.'s 128,000 b/d Benecia, Calif., refinery, and Tosco Corp.'s 126,000 b/d Martinez, Calif., refinery.
The first plant, Site IV, achieved turbine synchronization at yearend 1989. It has been undergoing permitting tests since then and is now at full load, performing final capacity tests for PG&E.
The Site 11 plant started up earlier this year, and Site V started up in mid-March. Both began PG&E capacity tests last month. All three are to be producing electricity at full load in time to meet PG&E's summer peak.
Sites I and III are under construction and planned for start-up by yearend.
CPC and GWF are owned by National Energy Partners (NEP), a joint venture of Community Energy Alternatives Inc., the independent power subsidiary of Public Service Enterprise Group which in turn is the Newark holding company for Public Service Electric & Gas of New Jersey, and the Harbert Power Group unit of Harbert Corp., Birmingham. NEP acquired the two companies from Allied Signal's Garrett Corp. in 1987.
National Energy Constructors built the plants, Ebasco Services Inc. furnished project engineering, and Harbert Operating Services provided start-up management.
ENVIRONMENTAL ADVANTAGES
The five plants are based on CPC's fines circulating fluidized bed combustor (Ficirc), which is designed to burn a wide range of fuels to generate steam for power and maintain low emissions of pollutants.
CPC and GWF teamed in the mid-1980s to develop California power plants based on Ficirc technology. GWF's Torrance, Calif., Ficirc pilot plant, which started up in 1986, was designated as best available control technology by California's South Coast Air Quality Management District.
Test burns in 1988 at the Torrance plant of high sulfur, high nitrogen content, delayed petroleum coke resulted in NOx and SO2 emissions reduced to less than 20 ppm and a calcium to sulfur ratio of 1.6-1.8:1
Those emissions levels are equivalent to ones in natural gas combustion in gas turbines with water injection, CPC said.
Each plant can burn auxiliary fuels such as coal or oil as much as 25% of its annual fuel take. Oil is the start-up fuel.
THE TECHNOLOGY
Ficirc combines the hot solids recycling of an entrained fluidized bed with the high turbulence and heat transfer of a deep, dense bubbling bed. The hybrid design results in combustion efficiency of more than 99% and reductions of sulfur dioxide and nitrogen oxides of more than 90%.
In the plants, petroleum coke is combined with limestone and ammonia to reduce emissions of NOx and SO2. A plant is designed to burn 14,600 lb/hr of petroleum coke at 1,500 psi and 1,000 F.
A rapid upflow of air suspends the mix in a fluidized state during combustion. Boiler tubes within the fluid bed are placed horizontally to cut erosion and ease removal. Hot cyclones are used to capture unburned fines and unreacted calcium oxide for return to the fluid bed. This allows virtually complete combustion and use of reactant limestone sorbent.
The boiler superheater, convection, and economizer sections are combined in a stacked module design external to the fluid bed. This results in a lower plant profile, lower cost maintenance platforms, and virtual elimination of field welding.
Water is then pumped through the system to be converted to steam at 166,000 lb/hr. The steam drives a turbine generator that produces 19,700 kw of electricity. Of that, 17,200 kw is fed into PG&E's power grid and the remainder is used onsite.
Resulting ash is stored onsite and sold to cement and building material manufacturers.
PETROLEUM COKE MARKET
CPC pointed out that more than 22 million tons/year of petroleum coke are produced in the U.S.
About 20-25% of that volume is consumed domestically, mainly delayed coke with a sulfur content of about 1-7%, it said.
As the proportion of heavier crudes sharply increased in U.S. refineries feedstocks, production of petroleum coke in the U.S. jumped to 21.9 million metric tons in 1988 from less than 5 million metric tons in 1960.
The current supply of U.S. coke is enough to generate 7-10 million kw of power, CPC said.
Most U.S. coke is exported to Europe and East Asia.
Cement manufacturers in Northwest Europe and the Mediterranean account for more than half the U.S. exports of coke to Europe. Japan, however, is the biggest single importer of U.S. coke, used mainly in small industrial boilers or steel manufacture.
Prices for high sulfur petroleum coke exports from the U.S. Gulf Coast have been weak for some time, currently about $19/metric ton, CPC said.
Beyond its premium use in aluminum smelting, demand for petroleum coke hinges on its price relative to other fuels, mainly coal. Tracking the world spot price of steam coal, petroleum coke is sold mainly into the export market in relatively small cargoes as needed without long term contracts, CPC said.
COKE PROS, CONS
Petroleum coke's high heating value-14,500 BTU/lb vs. 14,000 BTU/lb for bituminous coal, 9,600 BTU/lb for low quality coal, and 4,500 BTU/lb for wood-ordinarily would make it an attractive boiler fuel.
However, petroleum coke has a high sulfur content at 1-5 lb/MMBTU, which limits its use in standard combustion systems because of potential high SO2 emissions and scrubbing costs. It also features a low volatility content at 5-10 wt %, which often calls for cofiring with other fuels to maintain smooth combustion in most boiler systems.
In addition, petroleum coke has a low inherent ash content and nitrogen levels comparable with coal.
Because of its low cost and high heating value, petroleum coke is competitive with residual oil and coal, even after allowing for transportation costs over long distances, CPC said.
The Harbert companies stepped up development of fluid coke combustion technology because future refinery upgrading will cut supplies of delayed coke and boost the supplies of fluid coke.
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