This invention relates to the field of industrial waste disposal, and more particularly, to the incineration of industrial waste streams in thermal oxidizers, furnaces, combustors, or incinerators (hereinafter individually and collectively referred to as xe2x80x9cincineratorsxe2x80x9d), in combination with or without a boiler, in industrial processing industries such as the chemical industry (e.g., industrial process pertaining to the production of acrylonitrile, acrylic acid and its esters, methacrylic acid and its esters, and vinyl chloride monomers), petroleum refining industry, petrochemical industry, pharmaceutical industry, and the food industry.
Waste streams that are generally subject to incineration may be produced in industries such as the chemical industry, petroleum refining industry, petrochemical industry, pharmaceutical industry, and the food industry. Such waste streams may be sludges, slurries, gases, liquids, oils or combinations thereof For example, chemical processes that produce waste streams that need to be disposed of include the production of acrylonitrile, methacrylic acid and its esters, acrylic acid and its esters, vinyl chloride monomer, phenol, synthesis gas, and ethylene. Some petroleum refining sources of waste streams include: hydrotreater purge gas; catalytic reformer overhead gas; and fuel gas from the stabilizer column. Chemical plant sources include: waste hydrogen streams; vent header streams; slop-oil streams; absorber and stripper column overhead streams; and effluents from waste water treatment systems.
An incineration process is a rapid oxidation process that releases energy that may or may not be harnessed to do useful work such as producing steam in a boiler. Although incineration processes can achieve high destruction efficiencies, these systems are typically expensive to operate due to the energy involved. Most importantly, incineration systems have secondary emissions associated with their operation that are heavily regulated by environmental agencies such as the Environmental Protection Agency (the xe2x80x9cEPAxe2x80x9d) and the Texas Natural Resources Conservation Commission (the xe2x80x9cTNRCCxe2x80x9d). Substances in incineration emissions that typically are regulated are: CO and NOx. CO2 is also a concern as it is a greenhouse gas. Generally, environmental regulations limit the amount of these substances that can be emitted from a company""s waste incineration process on an hourly basis. Thus, the goal when disposing of waste streams through incineration is to comply with the applicable environmental regulations while minimizing energy consumption so that the process is cost-effective. Conventional incineration systems for industrial waste streams have failed to meet this goal.
In heretofore known incineration systems, environmental regulatory specifications limit the operating conditions of the incineration process to specific operating conditions used during a xe2x80x9cstack test.xe2x80x9d Usually, the xe2x80x9cstack testxe2x80x9d is run in a worst case scenario. Therefore, the operating conditions such as temperature, fuel, and air that are dictated by the stack test are not sufficiently flexible to adjust to changes in the composition, feed rate or fuel value of the waste streams. Operating conditions based on this single xe2x80x9cworst casexe2x80x9d approach are seldom varied as they oftentimes are dictated by rigid environmental permit requirements. Further, there is little opportunity for change as stack tests are performed infrequently. While this approach assures emissions compliance, its inflexibility also guarantees that the incinerator is always run at its most costly operating conditions.
In conventional industrial waste incineration processes operated at stack test operating conditions, a waste stream is generally combined in a furnace with a large amount of fuel, such as natural gas, and an excess of air. Because a large amount of fuel is used, the emissions that are produced from this conventional process usually comply with environmental regulations. However, this method is not cost-effective because natural gas, the primary fuel, is expensive. Also, because an excess of fuel is used, the temperature of the incinerator is very high, usually from about 1000xc2x0 F. (538xc2x0 C.) to about 2000xc2x0 F. (1076xc2x0 C.). These high temperatures, in combination with the nitrogen in the air feed to the system, create an undesirable amount of NOx, a heavily regulated emission substance.
Traditionally, efforts to minimize CO and NOx emissions from incineration systems have focused on the adjustment of air (e.g., temperature, flow, and distribution) in the system and optimization of its distribution. This has been done by monitoring the oxygen content of the emissions.
Measuring or monitoring the oxygen content of incineration emissions has been used in conventional systems as a standard feedback control, wherein adjustments to the air feed into the incineration system ultimately control the amount of CO in the incineration emissions. Insufficient air makes the system fuel-rich, which may pose an explosion hazard. While an excess of air avoids this problem and is favorable to achieving complete combustion, too much air results in excess NOx formation and requires greater energy consumption. Also, using more air means bigger fans, which in and of themselves are expensive. Heretofore known systems have not looked to temperature as the controlling variable to optimize the system; therefore, the conventional means to achieve optimization of the incineration process, i.e., by controlling the air feed through monitoring the oxygen content of the emissions, results in burdening the incineration process with excess air that must be heated and an excess formation of CO and NOx in the emissions. Operating costs are high and efficiency is low when control of the incineration process is solely limited to this method.
Another problem with some of the conventional incineration systems using the oxygen content of the emissions as a means to optimize the system is that, if the condition of the waste stream changes, the incineration system is unable to adapt to those changes optimally and reliably, resulting in inefficient and costly process performance and possibly regulatory noncompliance. Process parameters such as temperature in conventional systems are not adjusted to changes in the waste stream. Further, in conventional systems, the only means to address changes in the waste stream has historically been to add an excess of air to the system, which results in the disadvantages described above.
However, notwithstanding the awareness of these regulations, many of the conventional incineration methods have not been able to ensure their compliance on a cost-effective basis. Accordingly, the industrial processing industries would greatly welcome a method which not only controls emissions from industrial waste incineration processes such that compliance with environmental regulations is ensured, but also provides a method of incinerating waste wherein capital and operating costs are reduced significantly.
Therefore, one object of the present invention is to provide novel methods to optimize an industrial waste incineration process such that emissions from the process comply with environmental regulations and the process is cost-effective.
Another object of this invention is to provide novel methods which enable the incineration process to adapt quickly and accurately to changes in the waste stream (e.g., changes in its fuel value, temperature, feed rate, or composition), in a manner such that the emissions remain at or under the target level.
These and other objects that will become apparent to those skilled in the art upon reading this specification are based, in part, on the surprising discovery that modifying the operating temperature (hereinafter referred to as xe2x80x9cthe firebox temperaturexe2x80x9d) of the incinerator, in response to changes in the emissions products and waste streams, results in the ability to consistently control the incineration process and the resultant incineration emissions.
The present invention pertains to novel methods for incinerating industrial waste. In one embodiment, a method encompasses by the present invention includes the steps of:
(a) determining whether a waste stream is being fed into the incinerator,
(b) evaluating a CO emission rate to calculate the CO emissions rate minus a target CO rate (hereinafter xe2x80x9cxcex94COxe2x80x9d), and
(c) adjusting a firebox temperature of an incinerator in response to the xcex94CO calculation.
In another embodiment, a method encompassed by the present invention includes the steps of:
(a) determining whether a waste stream having a feed rate and a fuel content is being fed into an incinerator;
(b) measuring the feed rate of the waste stream to calculate a the mass flow rate of the waste stream at a time t1, minus the mass flow rate of the waste stream at a time t0, where t greater than t0 (hereinafter xe2x80x9cxcex94Mxe2x80x9d);
(c) adjusting a firebox temperature of the incinerator if xcex94M is greater than or less than 0;
(d) analyzing the energy content of the waste stream to calculate the energy content of the waste stream at a time t1, minus the energy content of the waste stream at a time t0, where t1 greater than t0 (hereinafter referred to as xe2x80x9cxcex94Exe2x80x9d);
(e) adjusting the firebox temperature of the incinerator if xcex94E is greater than or less than 0;
(f) evaluating a CO emission rate of the emission products to calculate a xcex94CO; and
(g) adjusting the firebox temperature of the incinerator if xcex94CO is greater than or less than 0.
One of the many advantages of the present invention is that less costly-fuel is now needed to maintain desirable destruction efficiency of waste. Accordingly, less energy is used in the incineration process; and therefore, the producer realizes a cost-savings. Another advantage of the present invention is that fewer undesirable emission products are generated because increases in air feed are avoided. Thus, the capital and operating costs associated with using a large amount of air in the system can be saved.
Other advantages of the present invention will be apparent to those of ordinary skill in the art in view of the following specification, claims and drawings.