Abstract

Incineration of waste natural gas products is not new to the oil and gas industry, however, significant improvements in incinerator design and technology have resulted in reduced costs and greater reliability. Because there is measurable, 99.99% combustion efficiency with no visible flame, black smoke or detectable odor, petroleum companies are now looking at incineration as a cost effective and environmentally responsible alternative to conventional flaring. Incineration also reduces greenhouse gas emissions.

WHAT IS INCINERATION?

Incineration is the complete combustion of waste natural gas streams, where the only emissions exiting from the incinerator stack are carbon dioxide and water. In situations where sulphur compounds such as hydrogen sulphide are present in the waste stream, sulphur dioxide will also exit the stack.

The combustion process within an incinerator results is a thorough mixing of the waste natural gas stream, with sufficient air, followed by the ignition process. The high temperatures reached in an incinerator ensure complete combustion of the waste stream.

SO HOW DOES AN INCINERATOR WORK?

The key components to an incinerator are: an air inlet, combustion chamber, burner assembly and the stack.

The self-aspirating combustion air inlet provides excess oxygen to the flame envelope area to ensure the complete combustion of the entire waste hydrocarbon product in the incinerator. In addition, this excess air cools the high flame temperature from 1700 ° C to an operating temperature of approximately 1200 ° - 1300 ° C that can be safely handled by the high quality ceramic refractory. The refractory linings that are utilized for a Questor Incinerator are designed for operating temperatures up to either 1430 °C or 1650 °C, depending upon the waste gas composition. Extensive testing has shown a mixing of 18 parts of air to 1 part of waste gas in the incinerator. This is approximately twice the amount of air actually required for complete combustion. The combustion gases exit the incinerator at approximately 1150 °C. This high exit temperature assists in the dispersion of the combustion products.

The Questor incinerator is capable of efficiently combusting multi-streams with varying pressure. Ideally these pressures are in the range of 5–30 psig but waste gas can be delivered to the incinerator at atmospheric pressure. If there is insufficient heating value in the waste gas stream it is necessary to add fuel gas to the stream to ensure complete combustion. The fuel gas enters the combustion chamber via specially configured and sized nozzles that cause a vigorous vortex to be developed. The result is a thorough mixing of the hydrocarbon stream with the air, thus ensuring complete combustion of the hydrocarbons.

The height of the incinerator stack is determined by two factors, the first is to ensure adequate retention time in the stack. Normal retention time is approximately onehalf second and will ensure complete combustion prior to the combusted products exiting the incinerator stack. The second parameter that governs stack height is provision for adequate SO2 dispersion, where the waste gas is sour. In Western Canada, the objective in SO2 dispersion is to ensure that in the worst case scenario, the ground level SO2 levels do not exceed 450 mg/m3.

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