PROCESSES FOR PRODUCING AND USING BROMINE PRODUCTS SUITABLE FOR REDUCING MERCURY EMISSIONS DURING COAL COMBUSTION

BACKGROUND

[0001] In 2005, the EPA issued the Clean Air Mercury Rule to cap and reduce mercury emissions from coal-fired power plants. This rule, combined with the EPA's Clean Air Interstate Rule (CAIR), will require significant reduction in mercury emissions from coal-fired power plants as early as 2010.

[0002] The Department of Energy has presented information from several studies that indicate mercury emissions during combustion of coal fuels can be lowered by treatment of the coal fuel stocks with low levels of bromine. [0003] Brines that are produced in several areas of the world contain substantial quantities of bromide salts, such as sodium bromide. Bromine can be recovered from such brines by treatment with chlorine to oxidize the bromide to bromine. Processes for electrolytic conversion of bromide to bromine are also known; but electrolytic conversion is an expensive alternative to the aforedescribed process. Catalytic oxidation of bromide to bromine by use of oxygen or air mixtures has been reported; but no successful, economic, commercial operation is in place today. [0004] Brominated flame-retardant materials (BFRs), which are designed to release HBr upon heating, are used in a multitude of consumer products, including without limitation, plastic covers of television sets, phones, other electronic equipment, carpets, paints, upholstery, clothing, and kitchen appliances. In computers, BFRs are used, e.g., in printed circuit boards, in connectors, in plastic covers, and in cables. All of these items have limited useful lives; and disposal and/or recycle of these types of materials is a well known issue.

[0005] Given the foregoing, and the fact that there is a finite supply of elemental bromine, it would be commercially beneficial to have methods for using otherwise discardable BFRs as alternative sources of bromine for use in minimizing mercury emissions from coal fuel stocks.

THE INVENTION

[0006] This invention meets the above-described needs by providing methods for using bromine available from brominated fiame-retardant materials (BFRs), e.g., plastics, to minimize mercury emissions from coal fuel stocks. [0007] According to this invention, BFRs are heated to cause the release of bromine as hydrogen bromide (HBr). At least some of the HBr driven off of heated BFRs can be converted to elemental bromine; at least some HBr, and/or at least some elemental bromine, can be treated with lime (CaO) to generate calcium bromide; and either the bromine or the calcium bromide can be used as the mercury-emission reduction treatment for coal fuel stocks. Additionally, at least some of the HBr and/or bromine can be combined with lime as the mercury-emission reduction treatment for coal fuel stocks. When BFRs are heated such that substantially all bromine contained in the BFRs are released as HBr, the BFRs can be used as fuel in conventional power generation equipment, but typically cannot be used as the mercury-emission reduction treatment for coal fuel stocks. When heating time is shorter, or process temperatures are lower, than those required to drive off substantially all of the bromine from the BFRs, or because of other factors, the BFRs retain reduced amounts of bromine. BFRs containing reduced amounts of bromine can be used as the mercury-emission reduction treatment for coal fuel stocks.

[0008] Processes are provided for producing calcium bromide from a brominated flame-retardant material, such processes comprising: a) heating the brominated flame- retardant material to at least about 100 ⁰ C; b) recovering HBr released from the brominated flame-retardant material during heating; and c) combining the HBr with CaO in a twin-screw extruder to produce an extruded stream comprising CaBr ₂ . Also provided are processes for producing calcium bromide from a brominated flame- retardant material, such processes comprising: a) heating the brominated flame- retardant material to at least about 100 ⁰ C; b) recovering HBr released from the brominated flame-retardant material during heating; d) converting the HBr to Br ₂ ; c) combining the Br ₂ with CaO in a twin-screw extruder to produce an extruded stream comprising CaBr ₂ . Also provided are such processes, wherein the HBr is converted to Br ₂ by a process comprising: a) combining at least the HBr and oxygen at a temperature higher than about 315 ⁰ C in the presence of a cerium-containing compound to produce a product stream comprising Br ₂ and H ₂ O; and b) cooling the product stream

directly with a cooling stream comprising water. Also provided are such processes, wherein the HBr is converted to Br ₂ by a process comprising: a) heating at least the HBr and oxygen directly with steam to a temperature higher than about 315 ⁰ C; b) placing at least the heated HBr and oxygen in the presence of a cerium-containing compound to produce a product stream comprising Br ₂ and H ₂ O; and c) cooling the product stream directly with a cooling stream comprising water. Also provided are such processes, wherein the HBr is converted to Br ₂ by a process comprising: a) heating the HBr directly with steam to a temperature higher than about 315°C; b) combining at least oxygen and the heated HBr at a temperature higher than about 315°C in the presence of a cerium-containing compound to produce a product stream comprising Br ₂ and H ₂ O; and c) cooling the product stream directly with a cooling stream comprising water. Processes are provided for conjointly recovering bromine values from a brominated flame retardant material and reducing mercury emissions from coal during combustion, the processes comprising: a) heating the brominated flame-retardant material to at least about 10O ⁰ C; b) recovering HBr released from the brominated flame-retardant material during heating; and c) combining the HBr and the coal either prior to or during combustion. Processes are provided for conjointly recovering bromine values from a brominated flame retardant material and reducing mercury emissions from coal during combustion, the processes comprising: a) heating the brominated flame-retardant material to at least about 10O ⁰ C; b) recovering HBr released from the brominated flame-retardant material during heating; c) combining the HBr with CaO in a twin-screw extruder to produce an extruded stream comprising CaBr ₂ ; and d) combining the stream comprising CaBr ₂ and the coal either prior to or during combustion. Processes are provided for conjointly recovering bromine values from a brominated flame retardant material and reducing mercury emissions from coal during combustion, such processes comprising: a) heating the brominated flame-retardant material to at least about 100°C; b) recovering HBr released from the brominated flame-retardant material during heating; c) converting the HBr to Br ₂ ; and d) combining the Br ₂ and the coal either prior to or during combustion. Processes are provided for conjointly recovering bromine values from a brominated flame retardant material and reducing mercury emissions from coal during combustion, such processes comprising: a) heating the brominated flame-retardant material to at least about 10O ⁰ C; b) recovering HBr released from the brominated flame-retardant material during heating; c) converting the

HBr to Br ₂ ; d) combining the Br ₂ with CaO in a twin-screw extruder to produce an

extruded stream comprising CaBr ₂ ; and e) combining the CaBr ₂ and the coal either prior to or during combustion. In such processes, the product stream can be cooled to produce a liquid product stream.

[0009] As used herein, heating or being heated "directly with" steam means that whatever is being heated is contacted by at least a portion of the steam, for example, by injecting steam into the stream comprising HBr, into the stream comprising oxygen, into both such streams, or into a combination of both such streams,

[0010] As used herein, cooling or being cooled "directly with" a cooling stream means that whatever is being cooled is contacted by at least a portion of the cooling stream, for example, by injecting the cooling stream into the product steam.

Heating of BFRs to Cause Release of HBr

[0011] BFRs can be heated rapidly (e.g., at rates of about 10°C/s) to high temperatures, e.g., about 227 ⁰ C to about 427°C and held at such temperatures as needed, to remove essentially all bromine from the BFR material matrix in the form of

HBr.

[0012] BFRs can also be heated rapidly (e.g., at rates of about 10°C/s) to temperatures of about 100 ⁰ C to about 227 ⁰ C, and held at such temperatures as needed, to remove some bromine from the BFR material matrix in the form of HBr, yet leave some bromine in the BFR material matrix.

[0013] One skilled in the art has the knowledge and skills to determine for any particular BFR, at what heating rate, to what temperature(s), and for how long the BFR needs to be heated to release the amount of HBr and/or retain the amount of bromine desired for the desired application.

Conversion of HBr to Elemental Bromine

[0014] Bromine can be recovered from HBr by methods well known to those skilled in the art, e.g., by using a steaming out process, by oxidation with chlorine, by oxidation with air/oxygen, etc. In particular, bromine can be recovered from HBr by a process whereby a stream comprising HBr is combined with a stream comprising oxygen at a temperature higher than about 315°C in the presence of a catalyst, e.g., a cerium- containing compound such as a cerium bromide catalyst on a zirconia-containing support, to produce a product stream comprising Br2 and H2O; and the product stream

is cooled directly with a cooling stream comprising water; or by such a process whereby the stream comprising HBr and/or the stream comprising oxygen is heated by direct contact with steam In such a process where direct heating with steam is used, use of heat exchangers can be avoided; this is beneficial because such heat exchangers would have to be built from expensive materials able to withstand the corrosive streams being processed. In processes of this invention, at least HBr and oxygen can be combined in the presence of a cerium-containing compound, e.g., at at least about 315°C (600T) to about 1000 ⁰ C (1832°F), or at at least about 315°C (600 ⁰ F) to about 538°C (1000 ⁰ F). As will be familiar to those skilled in the art, the upper temperature can be limited by the ability of the cerium-containing compound and/or of the processing equipment to withstand the temperature of operation. Cerium-containing compounds useful in processes of this invention can be any suitable cerium-containing compound. Such cerium-containing compounds are used as catalysts. Suitable catalysts are described, e.g., in US Patent No. 5,366,949 (Schubert), and include cerium bromide, cerium oxide, and the like. A suitable catalyst composition can comprise cerium bromide on zirconia containing supports.

Treatment of Br2/HBr with Calcium Oxide to Produce Calcium Bromide [0015] Either HBr or Br2 can be treated with lime (CaO) to generate calcium bromide, by means known to those skilled in the art. In particular, a stream comprising HBr or Br ₂ from any of the processes described herein can be combined with a stream comprising CaO and mixed in a twin-screw extruder to produce an extruded stream comprising calcium bromide. The stream comprising HBr or Br ₂ and the stream comprising CaO can be combined in the twin-screw extruder or can be combined to form a mixed product stream, which mixed product stream is passed through a twin- screw extruder to produce an extruded stream comprising calcium bromide.

Treatment of Coal to Reduce Mercury Emissions During Combustion

[0016] Elemental bromine, HBr, or calcium bromide, either together or separately, can be added to coal either before or during coal combustion to reduce mercury emissions during combustion.

[0017] When a BFR heated according to this invention retains in its matrix at least a sufficient amount of elemental bromine to affect mercury emissions from coal, the

matrix can be utilized as fuel in standard, conventional power generation equipment, either as the primary fuel or as a coal additive to reduce mercury emissions. [0018] Elemental bromine and/or HBr, either together or separately, can be combined with calcium oxide and added to coal either before or during combustion to reduce mercury emissions. When HBr and calcium oxide are combined directly with the coal, no isolation of HBr streams is required and essentially the whole operation is handled in one combustion unit fitted with suitable mixing equipment. [0019] It is to be understood that the reactants and components referred to by chemical name or formula anywhere in the specification or claims hereof, whether referred to in the singular or plural, are identified as they exist prior to being combined with or coming into contact with another substance referred to by chemical name or chemical type (e.g., another reactant, a solvent, or etc.). It matters not what chemical changes, transformations and/or reactions, if any, take place in the resulting combination or solution or reaction medium as such changes, transformations and/or reactions are the natural result of bringing the specified reactants and/or components together under the conditions called for pursuant to this disclosure. Thus the reactants and components are identified as ingredients to be brought together in connection with performing a desired chemical reaction or in forming a combination to be used in conducting a desired reaction. Accordingly, even though the claims hereinafter may refer to substances, components and/or ingredients in the present tense ("comprises", "is", etc.), the reference is to the substance, component or ingredient as it existed at the time just before it was first contacted, combined, blended or mixed with one or more other substances, components and/or ingredients in accordance with the present disclosure. Whatever transformations, if any, which occur in situ as a reaction is conducted is what the claim is intended to cover. Thus the fact that a substance, component or ingredient may have lost its original identity through a chemical reaction or transformation during the course of contacting, combining, blending or mixing operations, if conducted in accordance with this disclosure and with the application of common sense and the ordinary skill of a chemist, is thus wholly immaterial for an accurate understanding and appreciation of the true meaning and substance of this disclosure and the claims thereof. As will be familiar to those skilled in the art, the terms "combined", "combining", and the like as used herein mean that the components that are "combined" or that one is "combining" are put into a container with each other.

Likewise a "combination" of components means the components having been put together in a container.

[0020] While the present invention has been described in terms of one or more preferred embodiments, it is to be understood that other modifications may be made without departing from the scope of the invention, which is set forth in the claims below.