WO1996004508A1 - REDUCTION DES EMISSIONS DE NOx DANS UN PROCEDE D'INCINERATION A LIT FLUIDISE - Google Patents

REDUCTION DES EMISSIONS DE NOx DANS UN PROCEDE D'INCINERATION A LIT FLUIDISE Download PDF

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Publication number
WO1996004508A1
WO1996004508A1 PCT/US1995/000438 US9500438W WO9604508A1 WO 1996004508 A1 WO1996004508 A1 WO 1996004508A1 US 9500438 W US9500438 W US 9500438W WO 9604508 A1 WO9604508 A1 WO 9604508A1
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WO
WIPO (PCT)
Prior art keywords
urea
fluidized bed
bed
emissions
dry
Prior art date
Application number
PCT/US1995/000438
Other languages
English (en)
Inventor
Lewis W. Clark
Richard L. Samu
Original Assignee
Dorr-Oliver Incorporated
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Dorr-Oliver Incorporated filed Critical Dorr-Oliver Incorporated
Publication of WO1996004508A1 publication Critical patent/WO1996004508A1/fr

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
    • F23G5/00—Incineration of waste; Incinerator constructions; Details, accessories or control therefor
    • F23G5/30—Incineration of waste; Incinerator constructions; Details, accessories or control therefor having a fluidised bed
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23J—REMOVAL OR TREATMENT OF COMBUSTION PRODUCTS OR COMBUSTION RESIDUES; FLUES 
    • F23J7/00—Arrangement of devices for supplying chemicals to fire
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
    • F23G2209/00—Specific waste
    • F23G2209/12—Sludge, slurries or mixtures of liquids

Definitions

  • the invention is directed to the reduction of NO x levels in the flue gas from fluidized bed incinerators, particularly fluidized bed incinerators of the bubbling bed type.
  • Fluidized bed reactors are well-known means for generating heat and, in various forms, can carry out the processes of drying, roasting, calcining, incineration and heat treatment of solids in the chemical, metallurgical and other material processing fields. They are also used for the generation of hot gases, including steam, for use in driving electric power generation equipment, for process heat, for space heating, or for other purposes.
  • Fluidized bed reactors typically comprise a vessel having a substantially horizontal air distributor or constriction plate, which supports a bed of particulate solids in the reaction chamber and separates the reaction chamber from a windbox below the air distributor. Combustion air is introduced into the windbox and passes through the air distributor in sufficient volume to achieve a gas velocity that expands or fluidizes the solids bed, suspending the particulate solids of the bed in the flowing air stream and imparting to the individual particles a continuous random motion.
  • a fluidized bed in appearance and properties resembles a boiling liquid.
  • Conducting a combustion reaction in a fluidized bed has important advantages which include attainment of a substantially uniform bed temperature, combustion at relatively low temperatures, say 1350°-l 700°F, and a high heat transfer rate.
  • Nitrogen oxides are generated when fuel is burned, both from thermal fixation of nitrogen in the air and from conversion of nitrogen present in the fuel.
  • the former reaction is favored at high temperatures (above 1800°F) while the latter occurs at all temperatures.
  • the problem of NO x reduction in flue gas has hitherto been addressed by injection of ammonia into the effluent stream with and without catalysts.
  • U.S. Patent No. 3,900,554 suggests non-catalytic removal of NO x from flue gases by injecting ammonia into a gas stream at a temperature in the range 1600°-2000°F.
  • U.S. Patent 4,719,092 calls for reducing the concentration of NO x in oxygen-rich combustion effluents by injecting an aqueous solution of urea and an oxygenated hydrocarbon into the effluent at a temperature above 1600°F.
  • U.S. Patent No. 4,756,890 suggests injection of ammonia or an ammonia precursor into the gas stream within a high temperature cyclone separator at a location where there is a strong vortex region to obtain an efficient mixing of the NO x reducing agent and the combustion product flue gas.
  • This arrangement is particularly suitable for those fluidized bed reactors of the circulating bed type where large volumes of gas and solids are returned to the combustion reactor through a cyclone. It is not suitable for fluidized bed reactors of the bubbling bed type serving as incinerators because the incinerators generally do not employ cyclone separators. There is continuing interest in providing more convenient and effective methods for introducing NO x reducing compounds into incinerators.
  • Figure 1 is an elevational view, partially in section, of a fluidized bed incinerator of the bubbling bed type in which the process of the invention can be carried out.
  • Figure 2 is a graph in which the ppm of NO x generated is plotted as the flow of urea granules or prill in pounds per minute is increased over time.
  • Figure 3 is a graph in which ppm of NO x generated is plotted as the flow of urea solution in gallons per minute is increased over time.
  • the waste water sludge has a consistency resembling a wet peat moss or damp soil and pumping of this semi-solid (about 12% by weight solids) is accomplished using a progressive cavity type pump.
  • the additions of urea and calcium nitrate were sprinkled into the sludge as it reached the pump.
  • the treated sludge moved to the incinerator through a pipe about 100 feet long, taking about one hour in travel time to reach the incinerator.
  • both additions, i.e., of urea and calcium nitrate
  • added in this manner greatly increased NO x emissions from the incinerator.
  • NSR normal stoichiometric ratio
  • NSR is defined as the actual mole ratio of urea to NO x formed divided by the theoretical stoichiometric ratio, which is 0.5 for the reaction between urea and NO x . Therefore, an NSR of 1 means that the actual mole ratio of urea to NO x equals the theoretical stoichiometric ratio of 0.5 (0% excess urea).
  • An NSR of 2 means that urea is being fed at 100% excess, NSR of 3 implies 200% excess urea, etc.
  • the dry urea was continuously introduced into the bubbling bed during the test runs. Baseline NO x levels were established at the beginning and end of the complete test run. Figure 2 indicates that as the rate of urea introduction into the bed (Ib/min) increased, the ppm NO x levels decreased. Table 4 summarizes the results of the dry urea in-bed testing. The data indicate that as the level of dry urea introduced into the bed increased (i.e. Ib/min, NSR) the % NO x reduction increased.
  • a 15% (by wt) solution of urea in water was prepared and introduced into a bed-directed oil gun by a positive displacement chemical metering pump. A single feed point independent of the sludge feed point was used.
  • the sludge feed was a primary/secondary blend (61/39 dry weight basis) .
  • primary sludge differs from secondary sludge in that primary sludge is essentially a raw sludge whereas secondary sludge is a waste-activated sludge. Tests were conducted using either natural gas or No. 2 oil as auxiliary fuel. Once a baseline
  • a 30% (by wt) solution of urea in water was also prepared and injected into the bed.
  • the conditions were the same as the 15% solution test runs except decreasing flowrates of 0.5, 1.0, and 1.5 gpm were used.
  • the results obtained using natural gas as auxiliary fuel are presented in Table 5. As the flowrate decreased from 1.5 to 0.5 gpm, the ppm NO x levels increased.
  • Table 5 summarizes the results of the urea solution in-bed testing.
  • the data indicate that as the amount of urea introduced into the bed increased (i.e. gpm/NSR), the % NO x reduction increased.
  • the data suggest that the same NO x reduction levels can be attained (at the same NSR levels) when using either a 15% or 30% urea solution.
  • a 30% solution of urea in water is recommended since it can be introduced at half the flowrate (gpm) of a 15% solution thereby resulting in less bed quench.
  • aqueous urea solution directly into the bubbling bed of a fluidized bed incinerator, at a separate feed point independent of the sludge feed point, provides an oxidizing environment for the addition which enhances urea's effectiveness in reducing NO x .
  • the data indicates that there is no major advantage of urea in dry form over urea solutions with respect to NO x reduction (i.e., similar NO x reductions can be achieved at equivalent NSR values). However, it is usually more convenient to supply urea in the form of an aqueous solution.
  • a fluidized bed reactor 10 is shown having a vessel wall 11 which comprises a steel shell 13 and a refractory lining 14.
  • the reactor 10 is supported by grillage beams 36 which rest on a concrete pad or foundation 38.
  • the reaction chamber 16 in the main portion of the fluid bed reactor 10 is separated from the windbox 17 in the lower portion of the fluid bed reactor by a perforated steel constriction plate or the perforated refractory dome 21 as shown.
  • a steel constriction plate is suitable for cold windbox operation while the perforated refractory dome is used when the incoming air is heated; that is, for "hot windbox" operation.
  • the freeboard region of the reaction chamber is designated by the reference character 16.
  • the refractory dome 21 is provided with a number of tuyeres 22 for providing communication between the windbox 17 and the reaction chamber 16.
  • a conduit 27 is provided for introducing feed stock into the reaction chamber 16.
  • a fluidized bed 24 is illustrated in the reaction chamber 16 and a conduit 26 is provided for draining the bed material or removal of solid particulate products if required.
  • a conduit 29 is provided for supplying air to the windbox 17.
  • a duct 34 is provided for the off-gases emanating from the reaction chamber 16.
  • a conduit 28 may be provided for introducing secondary air into the reaction chamber 16.
  • reaction A above dominates to the extent that 90- 95% of the urea is involved in this reaction.
  • the fluidized bed reactor 10 has within the reaction chamber
  • Combustion takes place primarily in the expanded bed 24 at temperatures of 1350°F to 1600°F and at the level of secondary air introduction and there above in reaction chamber 16 where gases and suspended fine solid particles are burned at temperatures of 1350°F to 1700°F.
  • the sludge to be incinerated is supplied directly into the fluidized bed through conduit 27.
  • the urea is separately injected directly into the fluidized bed through supply conduit or hose 41. The amount of injected urea used is substantially in excess of that required to complete the desired reactions.
  • a fluidized bed reactor about 30 feet high and having a maximum diameter at the reaction chamber of about 27 feet is provided with a refractory combustion dome separating the reaction chamber from the windbox below.
  • a bed comprising inert material i.e. silica sand
  • inert material i.e. silica sand
  • it is fluidized in the combustion zone of the reaction chamber by introducing a flow of air from the windbox sufficient to establish an air flow of from 2.0 ft/sec to 4 ft/sec.
  • This air flow expands the charge in the reaction chamber and forms a fluidized bed of the bubbling bed type.
  • Waste material containing organics i.e., waste water sludge
  • the urea in granule form or as a solution is separately injected directly into the fluidized bed. Combustion of the organic material in the charge takes place at a temperature of from 1350°F to 1600°F. There is excess air present in the process so that emissions from the reactor contain about 4-10% by volume of oxygen.
  • the percent NO x reduction of which this process of urea injection is capable ranges from 25% up to about 70%.

Abstract

Dans un procédé d'incinération d'une boue d'eaux usées (24) dans un réacteur à lit fluidisé (10) du type à lit à bullage, de l'urée sous forme de granule ou en solution est injectée directement dans le lit fluidisé de bullage du réacteur (10) au travers d'un conduit (41) afin d'effectuer une réduction des émissions de NOx d'au moins 25 %.
PCT/US1995/000438 1994-08-03 1995-01-17 REDUCTION DES EMISSIONS DE NOx DANS UN PROCEDE D'INCINERATION A LIT FLUIDISE WO1996004508A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US28507194A 1994-08-03 1994-08-03
US08/285,071 1994-08-03

Publications (1)

Publication Number Publication Date
WO1996004508A1 true WO1996004508A1 (fr) 1996-02-15

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US1995/000438 WO1996004508A1 (fr) 1994-08-03 1995-01-17 REDUCTION DES EMISSIONS DE NOx DANS UN PROCEDE D'INCINERATION A LIT FLUIDISE

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WO (1) WO1996004508A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20130333597A1 (en) * 2012-04-19 2013-12-19 Degremont Methods and Systems for Flue Gas Denitrification

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4181705A (en) * 1978-08-18 1980-01-01 Chevron Research Company Purification of fluidized-bed combustion flue gas
US4208386A (en) * 1976-03-03 1980-06-17 Electric Power Research Institute, Inc. Urea reduction of NOx in combustion effluents
US5058514A (en) * 1989-10-18 1991-10-22 Mozes Miriam S Process for controlling acid gas emissions in power plant flue gases

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4208386A (en) * 1976-03-03 1980-06-17 Electric Power Research Institute, Inc. Urea reduction of NOx in combustion effluents
US4181705A (en) * 1978-08-18 1980-01-01 Chevron Research Company Purification of fluidized-bed combustion flue gas
US5058514A (en) * 1989-10-18 1991-10-22 Mozes Miriam S Process for controlling acid gas emissions in power plant flue gases

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20130333597A1 (en) * 2012-04-19 2013-12-19 Degremont Methods and Systems for Flue Gas Denitrification
US10458650B2 (en) * 2012-04-19 2019-10-29 Degremont Methods and systems for flue gas denitrification

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