Petroleum coke calcining is a process whereby green or raw petroleum coke is thermally upgraded to remove associated moisture and volatile combustion matter (VCM) and to otherwise improve critical physical properties (e.g., electrical conductivity, real density and oxidation characteristics). The calcining process is essentially a time-temperature function with the most important control variables being heating rate, VCM/air ratio, and final calcinations temperature. To obtain the calcined coke properties required by the carbon and graphite industries, the coke must be subjected to temperatures of 2200-2450°F or higher to refine its crystalline structure. Calcined coke is vital to the aluminum industry where it is used to produce carbon anodes for aluminum production. It is also widely used as recarburizer in the iron and steel industry.
Petroleum coke kilns are an example of high-temperature (1800-2000°F) exhaust recovery of heat that would otherwise be wastefully released into the atmosphere. The steam and power produced have no associated emissions, and in most cases, these systems do not require auxiliary firing because of the high-quality exhaust heat available.
BenefitsThe implementation of CHP, compared to conventional processes, yields significant energy, environmental, and economic benefits, including the following:
- Reduced fuel consumption of 25%–50%
- Enhanced specific production rates of 50%–100%
- Energy savings of 0.94 trillion Btu per year for a production unit of 100,000 metric tons per year
- Lowered environmental impact resulting from improved combustion
For comparison's sake, heat recovered from one petroleum coke kiln (100,000 metric tons/yr capacity) could
- heat 20,000 U.S. homes
- power 10,000 U.S. homes
- avoid 275,000 barrels of crude oil import/year
- offset 100,000 tons CO2 emission/year
Case study:
Port Arthur Steam Energy LP (PASE) is one of the largest examples of coke calcination and CHP integration in the United States. This waste heat recovery project, located in Port Arthur, Texas, achieved commercial operation in August, 2005. PASE produces approximately 450,000 lb/hr of high pressure steam from flue gas heat recovered from three petroleum coke calcining kilns at the Oxbow Corp. calcining facility. A majority of the steam is sold to the neighboring Valero-Port Arthur refinery for process use, with the balance used to produce 5 MW of electricity. The power generated is used by Oxbow and PASE to serve internal load requirements, with excess sold to the utility grid via Entergy.
By capturing 1800-2000ºF heat that would otherwise be wasted out of the kiln stacks, the steam and power produced have no associated emissions. The project recovers nearly 5 trillion BTUs/year, displacing natural gas combustion in fired boilers at the refinery. It is estimated that PASE offsets over 200 tons/yr of NOx and over 280,000 tons/yr of greenhouse gases (CO2) that would otherwise be emitted to the atmosphere in supplying this energy.
The 2004-05 refurbishment and plant upgrade project included a new distributed control system, heightened stacks, boiler tube and refractory replacement, water treatment system upgrade, and the installation of multiclone particulate removal systems to each boiler. Integral Power, LLC (Houston, TX) led the development and execution effort for this unique brownfield project, with funding provided by American Industrial Partners. PASE contracts with North American Energy Services for day-to-day operations and maintenance of the facility, which includes 21 full time employees.
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