NZ746788A - Process And System For Reducing Ringing In Lime Kilns - Google Patents
Process And System For Reducing Ringing In Lime KilnsInfo
- Publication number
- NZ746788A NZ746788A NZ746788A NZ74678818A NZ746788A NZ 746788 A NZ746788 A NZ 746788A NZ 746788 A NZ746788 A NZ 746788A NZ 74678818 A NZ74678818 A NZ 74678818A NZ 746788 A NZ746788 A NZ 746788A
- Authority
- NZ
- New Zealand
- Prior art keywords
- kiln
- temperature
- chamber
- insertion location
- ncgs
- Prior art date
Links
- 238000000034 method Methods 0.000 title claims abstract description 45
- 230000001603 reducing Effects 0.000 title claims abstract description 15
- 235000008733 Citrus aurantifolia Nutrition 0.000 title description 59
- 235000015450 Tilia cordata Nutrition 0.000 title description 59
- 235000011941 Tilia x europaea Nutrition 0.000 title description 59
- 239000004571 lime Substances 0.000 title description 59
- 238000001354 calcination Methods 0.000 claims abstract description 143
- 239000007789 gas Substances 0.000 claims abstract description 40
- 238000010438 heat treatment Methods 0.000 claims abstract description 17
- 238000009825 accumulation Methods 0.000 claims abstract description 16
- 238000011144 upstream manufacturing Methods 0.000 claims abstract description 9
- 238000003780 insertion Methods 0.000 claims description 66
- 239000003546 flue gas Substances 0.000 claims description 21
- 239000000376 reactant Substances 0.000 claims description 18
- GQPLMRYTRLFLPF-UHFFFAOYSA-N nitrous Oxide Chemical class [O-][N+]#N GQPLMRYTRLFLPF-UHFFFAOYSA-N 0.000 claims description 15
- 238000001035 drying Methods 0.000 claims description 12
- XSQUKJJJFZCRTK-UHFFFAOYSA-N urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 claims description 12
- UGFAIRIUMAVXCW-UHFFFAOYSA-N carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 claims description 10
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 10
- QGZKDVFQNNGYKY-UHFFFAOYSA-N ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims description 7
- 239000002826 coolant Substances 0.000 claims description 7
- 239000004202 carbamide Substances 0.000 claims description 6
- 230000001590 oxidative Effects 0.000 claims description 6
- 239000001301 oxygen Substances 0.000 claims description 6
- MYMOFIZGZYHOMD-UHFFFAOYSA-N oxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 claims description 6
- 229910052760 oxygen Inorganic materials 0.000 claims description 6
- 150000001875 compounds Chemical class 0.000 claims description 4
- 239000003795 chemical substances by application Substances 0.000 claims description 2
- 238000005245 sintering Methods 0.000 claims description 2
- 229910052500 inorganic mineral Inorganic materials 0.000 abstract description 2
- 239000011707 mineral Substances 0.000 abstract description 2
- MWUXSHHQAYIFBG-UHFFFAOYSA-N Nitrogen oxide Substances O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 62
- 244000089742 Citrus aurantifolia Species 0.000 description 59
- ODINCKMPIJJUCX-UHFFFAOYSA-N calcium monoxide Chemical compound [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 description 23
- 239000000446 fuel Substances 0.000 description 21
- 239000000126 substance Substances 0.000 description 16
- 230000035508 accumulation Effects 0.000 description 14
- 238000006243 chemical reaction Methods 0.000 description 13
- HEMHJVSKTPXQMS-UHFFFAOYSA-M sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 12
- 239000000292 calcium oxide Substances 0.000 description 11
- 238000004537 pulping Methods 0.000 description 10
- 239000000463 material Substances 0.000 description 9
- VTYYLEPIZMXCLO-UHFFFAOYSA-L calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 8
- 235000012255 calcium oxide Nutrition 0.000 description 8
- OKKJLVBELUTLKV-UHFFFAOYSA-N methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 8
- 239000011734 sodium Substances 0.000 description 8
- 229910052708 sodium Inorganic materials 0.000 description 8
- 239000000047 product Substances 0.000 description 7
- 238000011084 recovery Methods 0.000 description 7
- KEAYESYHFKHZAL-UHFFFAOYSA-N sodium Chemical compound [Na] KEAYESYHFKHZAL-UHFFFAOYSA-N 0.000 description 7
- 206010054107 Nodule Diseases 0.000 description 6
- 239000006227 byproduct Substances 0.000 description 6
- 241000779819 Syncarpia glomulifera Species 0.000 description 5
- 229940036248 Turpentine Drugs 0.000 description 5
- 238000002485 combustion reaction Methods 0.000 description 5
- 239000000203 mixture Substances 0.000 description 5
- 230000003647 oxidation Effects 0.000 description 5
- 238000007254 oxidation reaction Methods 0.000 description 5
- CBENFWSGALASAD-UHFFFAOYSA-N ozone Chemical compound [O-][O+]=O CBENFWSGALASAD-UHFFFAOYSA-N 0.000 description 5
- 239000000123 paper Substances 0.000 description 5
- 239000001739 pinus spp. Substances 0.000 description 5
- 238000007363 ring formation reaction Methods 0.000 description 5
- 229960003563 Calcium Carbonate Drugs 0.000 description 4
- BVKZGUZCCUSVTD-UHFFFAOYSA-N Carbonic acid Chemical compound OC(O)=O BVKZGUZCCUSVTD-UHFFFAOYSA-N 0.000 description 4
- WQOXQRCZOLPYPM-UHFFFAOYSA-N Dimethyl disulfide Chemical compound CSSC WQOXQRCZOLPYPM-UHFFFAOYSA-N 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 4
- 229910000019 calcium carbonate Inorganic materials 0.000 description 4
- 238000010411 cooking Methods 0.000 description 4
- 239000012530 fluid Substances 0.000 description 4
- 238000005755 formation reaction Methods 0.000 description 4
- 238000007710 freezing Methods 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- QMMFVYPAHWMCMS-UHFFFAOYSA-N methyl sulfide Chemical compound CSC QMMFVYPAHWMCMS-UHFFFAOYSA-N 0.000 description 4
- 150000002830 nitrogen compounds Chemical class 0.000 description 4
- 239000001272 nitrous oxide Substances 0.000 description 4
- 150000002927 oxygen compounds Chemical class 0.000 description 4
- CDBYLPFSWZWCQE-UHFFFAOYSA-L sodium carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 4
- NINIDFKCEFEMDL-UHFFFAOYSA-N sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 4
- 229910052717 sulfur Inorganic materials 0.000 description 4
- 239000011593 sulfur Substances 0.000 description 4
- 150000003464 sulfur compounds Chemical class 0.000 description 4
- 238000010257 thawing Methods 0.000 description 4
- 244000007645 Citrus mitis Species 0.000 description 3
- GRVFOGOEDUUMBP-UHFFFAOYSA-N Sodium sulfide Chemical compound [Na+].[Na+].[S-2] GRVFOGOEDUUMBP-UHFFFAOYSA-N 0.000 description 3
- 239000002585 base Substances 0.000 description 3
- 238000001311 chemical methods and process Methods 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 239000000428 dust Substances 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- PEDCQBHIVMGVHV-UHFFFAOYSA-N glycerine Chemical compound OCC(O)CO PEDCQBHIVMGVHV-UHFFFAOYSA-N 0.000 description 3
- 150000002484 inorganic compounds Chemical class 0.000 description 3
- 229910010272 inorganic material Inorganic materials 0.000 description 3
- 239000002655 kraft paper Substances 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 3
- 239000002245 particle Substances 0.000 description 3
- 239000002893 slag Substances 0.000 description 3
- 229910052979 sodium sulfide Inorganic materials 0.000 description 3
- 231100000331 toxic Toxicity 0.000 description 3
- 230000002588 toxic Effects 0.000 description 3
- AXCZMVOFGPJBDE-UHFFFAOYSA-L Calcium hydroxide Chemical compound [OH-].[OH-].[Ca+2] AXCZMVOFGPJBDE-UHFFFAOYSA-L 0.000 description 2
- 229910002089 NOx Inorganic materials 0.000 description 2
- 241001062472 Stokellia anisodon Species 0.000 description 2
- 238000007792 addition Methods 0.000 description 2
- LSNNMFCWUKXFEE-UHFFFAOYSA-M bisulfite Chemical compound OS([O-])=O LSNNMFCWUKXFEE-UHFFFAOYSA-M 0.000 description 2
- 239000000920 calcium hydroxide Substances 0.000 description 2
- 229910001861 calcium hydroxide Inorganic materials 0.000 description 2
- 238000010531 catalytic reduction reaction Methods 0.000 description 2
- 239000000356 contaminant Substances 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 230000000875 corresponding Effects 0.000 description 2
- RWSOTUBLDIXVET-UHFFFAOYSA-N dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 2
- 239000003344 environmental pollutant Substances 0.000 description 2
- 239000000835 fiber Substances 0.000 description 2
- 238000002309 gasification Methods 0.000 description 2
- 239000003292 glue Substances 0.000 description 2
- 229910000037 hydrogen sulfide Inorganic materials 0.000 description 2
- 229920005610 lignin Polymers 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- LSDPWZHWYPCBBB-UHFFFAOYSA-N methanethiol Chemical compound SC LSDPWZHWYPCBBB-UHFFFAOYSA-N 0.000 description 2
- 229910052813 nitrogen oxide Inorganic materials 0.000 description 2
- 231100000719 pollutant Toxicity 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 238000006722 reduction reaction Methods 0.000 description 2
- 239000011819 refractory material Substances 0.000 description 2
- 239000001187 sodium carbonate Substances 0.000 description 2
- 229910000029 sodium carbonate Inorganic materials 0.000 description 2
- 210000000009 suboesophageal ganglion Anatomy 0.000 description 2
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 2
- 239000005436 troposphere Substances 0.000 description 2
- 239000002023 wood Substances 0.000 description 2
- 241000609240 Ambelania acida Species 0.000 description 1
- 102100012550 CNGA1 Human genes 0.000 description 1
- 108060002029 CNGA1 Proteins 0.000 description 1
- 229910000975 Carbon steel Inorganic materials 0.000 description 1
- 241000196324 Embryophyta Species 0.000 description 1
- VTHJTEIRLNZDEV-UHFFFAOYSA-L Magnesium hydroxide Chemical compound [OH-].[OH-].[Mg+2] VTHJTEIRLNZDEV-UHFFFAOYSA-L 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- 240000008042 Zea mays Species 0.000 description 1
- 235000002017 Zea mays subsp mays Nutrition 0.000 description 1
- 239000002250 absorbent Substances 0.000 description 1
- 230000002745 absorbent Effects 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 238000003916 acid precipitation Methods 0.000 description 1
- 150000007513 acids Chemical class 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 238000005054 agglomeration Methods 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 239000000809 air pollutant Substances 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 150000001450 anions Chemical class 0.000 description 1
- 239000010905 bagasse Substances 0.000 description 1
- 239000002551 biofuel Substances 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- 239000011449 brick Substances 0.000 description 1
- 239000011575 calcium Substances 0.000 description 1
- 239000010962 carbon steel Substances 0.000 description 1
- 239000004568 cement Substances 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 239000003034 coal gas Substances 0.000 description 1
- 239000004567 concrete Substances 0.000 description 1
- 235000005822 corn Nutrition 0.000 description 1
- 235000005824 corn Nutrition 0.000 description 1
- 231100000078 corrosive Toxicity 0.000 description 1
- 231100001010 corrosive Toxicity 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- 230000001419 dependent Effects 0.000 description 1
- 238000007865 diluting Methods 0.000 description 1
- 230000003292 diminished Effects 0.000 description 1
- 230000003467 diminishing Effects 0.000 description 1
- 229910001873 dinitrogen Inorganic materials 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 239000010459 dolomite Substances 0.000 description 1
- 229910000514 dolomite Inorganic materials 0.000 description 1
- 230000003628 erosive Effects 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 238000004880 explosion Methods 0.000 description 1
- 239000000945 filler Substances 0.000 description 1
- 239000003517 fume Substances 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 239000005431 greenhouse gas Substances 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 125000004435 hydrogen atoms Chemical class [H]* 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 239000003949 liquefied natural gas Substances 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000000395 magnesium oxide Substances 0.000 description 1
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 235000010755 mineral Nutrition 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000006011 modification reaction Methods 0.000 description 1
- 239000003607 modifier Substances 0.000 description 1
- 239000003345 natural gas Substances 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 150000002894 organic compounds Chemical class 0.000 description 1
- 239000007800 oxidant agent Substances 0.000 description 1
- 239000005022 packaging material Substances 0.000 description 1
- 239000002006 petroleum coke Substances 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 238000002203 pretreatment Methods 0.000 description 1
- 102000004169 proteins and genes Human genes 0.000 description 1
- 108090000623 proteins and genes Proteins 0.000 description 1
- 238000000197 pyrolysis Methods 0.000 description 1
- 238000009877 rendering Methods 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 239000002002 slurry Substances 0.000 description 1
- 150000003385 sodium Chemical class 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- 150000003388 sodium compounds Chemical class 0.000 description 1
- 239000011343 solid material Substances 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 238000004901 spalling Methods 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 239000010907 stover Substances 0.000 description 1
- 239000005437 stratosphere Substances 0.000 description 1
- 238000005670 sulfation reaction Methods 0.000 description 1
- XTQHKBHJIVJGKJ-UHFFFAOYSA-N sulfur monoxide Chemical class S=O XTQHKBHJIVJGKJ-UHFFFAOYSA-N 0.000 description 1
- 229910052815 sulfur oxide Inorganic materials 0.000 description 1
- 150000003467 sulfuric acid derivatives Chemical class 0.000 description 1
- 239000003784 tall oil Substances 0.000 description 1
- -1 thiols Chemical class 0.000 description 1
- 150000003573 thiols Chemical class 0.000 description 1
- 239000004408 titanium dioxide Substances 0.000 description 1
- 238000004642 transportation engineering Methods 0.000 description 1
Abstract
This application discloses exemplary processes and systems for reducing mineral ring accumulation in calcination kiln. The processes and systems comprise inserting non-condensable gases (“NCGs”) in a preheating zone of a calcination kiln, upstream of the burner end. The pre-heating zone may be characterized by temperatures ranging from 1,300° F to 1,750° F. The system may desirably comprise a plenum for inserting the NCGs into the rotating calcination kiln at the pre-heating zone. racterized by temperatures ranging from 1,300° F to 1,750° F. The system may desirably comprise a plenum for inserting the NCGs into the rotating calcination kiln at the pre-heating zone.
Description
PROCESS AND SYSTEM FOR REDUCING RINGING IN LIME KILNS
BACKGROUND OF THE INVENTION
1. TECHNICAL FIELD
The present disclosure relates generally to pollution control and contaminant
management in elongate rotary calcination kilns and more particularly to reducing nitrogen oxides
(“NO ”) and diminishing mid-kiln mineral accumulation in lime mud kilns used for chemical
recovery in the pulp and paper industry.
2. RELATED ART
There are several ways to produce pulp on an industrial scale, and producers tend to
classify these methods into one of three general categories: chemical pulping, mechanical pulping,
and hybrid pulping. Hybrid pulping involves different aspects of both chemical and mechanical
pulping. Briefly, mechanical pulping often involves feeding lignocellulosic material (e.g. wood
chips, bagasse, corn stover, recycled paper, or other material comprising the protein lignin and
cellulosic polymers) through a series of refiner plates. The refiner plates grind the lignocellulosic
material to the desired pulp grade. Mill operators may further process this pulp into a number of
pulp-based products (e.g. paper, packaging material, absorbent filler, etc.); or the mill operators
may sell the pulp wholesale.
In chemical processes, mill operators treat lignocellulosic material with either strong
acids or strong bases to disassociate the lignin from the cellulosic fibers. Operators may then
separate, wash, and further process the cellulosic fibers into pulp or other pulp-based products.
Chemical process examples include the Kraft process (also known as the “sulfate process”), sulfite
process, soda pulping process, and the sulfite semi-chemical pulping process.
While the processing chemicals for each type of chemical process may vary, mill
operators frequently recover and recycle these process chemicals to operate the mill economically.
In the Kraft process for example, mill operators cook the lignocellulosic material with “white
liquor” in large pressurized digesters. The white liquor comprises sodium hydroxide (NaOH) and
sodium sulfide (Na2S). After cooking, a slurry of spent chemical liquor and rough pulp, having
inconsistent particle sizes, exits the digester. The spent chemical liquor is commonly known as
“black liquor” and comprises organic and inorganic compounds left over from the cooking process.
While the rough pulp is further processed, the chemical recovery process begins with
isolating, concentrating, and then transferring the black liquor into a chemical recovery boiler. The
chemical recovery boiler evaporates excess moisture and the inorganic compounds in the black
liquor undergo pyrolysis. These inorganic compounds accumulate as molten salts (“smelt”) at the
bottom of the recovery boiler and eventually flow into an adjacent dissolving tank. The dissolving
tank typically contains “weak wash” comprising the liquors used to wash lime mud and other
precipitates. Upon contacting the weak wash, the smelt reacts and mixes with the weak wash to
become “green liquor”. The green liquor contains the first component of white liquor, sodium
sulfide (Na S) and the byproduct sodium carbonate (Na CO ).
2 2 3
Operators then clarify and feed the green liquor into an agitator and add calcium oxide,
(CaO) and water. Calcium oxide is commonly known as “quicklime”. The quicklime
exothermically reacts with the water to produce calcium hydroxide, (Ca(OH) ). The calcium
hydroxide then reacts with the sodium carbonate in the green liquor to produce the other
component of white liquor, sodium hydroxide (NaOH) and the byproduct calcium carbonate
(CaCO3). Calcium carbonate is commonly known as “lime mud”.
At this stage, the lime mud precipitates out of the white liquor solution. Operators then
clarify and transfer the white liquor to a storage tank to await reuse in the Kraft process.
Meanwhile, operators wash and transfer the lime mud to a lime kiln for conversion back into
quicklime (i.e. calcium oxide (CaO)). With the recycled quicklime, the mill operators may
continue to treat green liquor and recover white liquor cost effectively.
A typical lime kiln consists of a long rotary cylindrical housing that defines a calcining
kiln chamber. The housing is tilted relative to the ground. A burner is placed in the bottom end
and an arrangement of chains is placed in the upper end. Lime mud comprising calcium carbonate
(CaCO ), sodium, and other impurities enters the kiln’s upper end with a moisture content of about
% to 30%. As the lime mud moves down the rotating housing toward the burner, the heat drives
off the moisture and preheats the lime mud to reaction temperatures using the residual heat in the
flue gases. The calcining reaction begins when the mud temperature reaches 1,400°F, but the
reaction proceeds well only after the mud reaches 1800°F. The reclaimed quicklime may be cooled
before exiting the bottom end of the kiln.
Chemical pulping also produces a variety of gaseous byproducts from several sources.
These gaseous byproducts frequently contain sulfur compounds, including thiols, which are
odorous and can be toxic. Collectively, these gaseous byproducts can be referred to as “non-
condensable gases” (“NCGs”) and typically comprise “total reduced sulfur (“TRS”) gases. The
digester produces NCGs during cooking and flash tanks release NCGs when concentrating black
liquor. Sources also include evaporators, turpentine systems, and condensate stripping systems.
NCGs may include for example, sulfur compounds such as hydrogen sulfide (H S), methanethiol
(CH S), dimethyl disulfide ((CH ) S ), and dimethyl sulfide ((CH ) S). These NCGs are inserted
4 3 2 2 3 2
into the lime kiln near the burner to oxidize the NCGs prior to exiting the kiln.
The chemical pulping process can also produce a number of condensable gases such as
ammonia (NH ), methanol (CH OH), and turpentine (C H ). These condensable gases are also
3 3 10 16
sometimes used as a fuel supplement in the lime kiln and may be added to the lime kiln at or near
the burner.
Sodium in the lime mud may react with the sulfur compounds in the NCGs in complex
chemistries to form mid-kiln rings that accumulate on the inner walls of the refractory material
inside the kiln. These mid-kiln rings can create temperature pockets along the length of the kiln
that adversely affect the calcining reaction. The mid-kiln rings also reduce the volume of the kiln
and cause reactant accumulation upstream of the rings, which can lead to an incomplete calcining
reaction and further ring growth. Additionally, the mid-kiln rings absorb heat from the kiln system,
thereby encouraging the operators to expend more energy to achieve the same results.
Prior attempts to reduce ring formation involved cooling kiln sections in which rings
were most likely to form, such as the lime kiln described in U.S. Pat. No. 4,767,323. The cooler
kiln sections would freeze the molten slag and cause the frozen slag to spall off the wall due to
differential thermal expansion. However, the spalled slag would fall into the lime bed and soon
re-melt, thereby contaminating the lime product.
Additionally, elongate rotary calcination kilns produce nitrogen oxides (“NO ”),
including nitric oxide (NO), nitrous oxide (N O) and dinitrogen dioxide (N O ). Nitrous oxide
2 2 2
(N2O) is “greenhouse gas” that reacts with air and ultraviolet (“UV”) light to create nitric oxide
(NO) and ozone (O ) in the troposphere (i.e. the portion of the atmosphere where people live and
breathe). UV light in the atmosphere can then convert nitric oxide (NO) back into nitrous oxide
(N O), thereby establishing the foundation for further ozone (O ) production. While the ozone
layer in the stratosphere helpfully absorbs most UV radiation reaching Earth from space, ozone
gas (O ) is nonetheless a strong oxidizing agent that is toxic to humans. Furthermore, ozone (O )
and NO and additional pollutants in the troposphere contribute to acid rain. Accordingly, many
governmental environmental protection agencies regulate the emissions of NOx.
It will be clearly understood that, if a prior art publication is referred to herein, this
reference does not constitute an admission that the publication forms part of the common general
knowledge in the art in Australia or in any other country.
SUMMARY OF THE INVENTION
In one aspect, the present invention provides an elongate rotary calcination kiln
system comprising:
a tubular housing having an outer shell and a refractory lining disposed within the outer
shell, the refractory lining defining a kiln chamber, the kiln chamber having a burner end, a feed
end distally disposed from the burner end, and a length extending between the burner end and the
feed end;
a plenum annularly disposed around the tubular housing, the plenum comprising a
plenum housing defining a plenum chamber annularly disposed around the tubular housing,
wherein the plenum chamber fluidly communicates with the chamber through an opening
disposed at an insertion location, at about two thirds the length of the kiln chamber as measured
from the burner end, wherein the plenum is configured to convey NCGs into the kiln chamber
through the opening at the insertion location, and wherein a temperature at the insertion location
is between 212 °F and 2,200 °F (between 100°C and about 1,204.44 °C).
In a second aspect, the present invention provides a process for reducing the
accumulation of mid-kiln rings in an elongate rotary calcination kiln comprising introducing
NCGs into an elongate rotary calcination kiln, at an insertion location downstream of a burner
end in a kiln chamber of an elongate rotary calcination kiln, wherein a temperature of the kiln
chamber at the insertion location is in a range of 212 °F to 2,200 °F (in a range of 100°C and
about 1,204.44 °C).
In a third aspect, the present invention provides a process for reducing the
accumulation of kiln rings in an elongate rotary calcination kiln comprising:
feeding a calcine reactant into an elongate rotary calcination kiln at a feed end of the
elongate rotary calcination kiln;
oxidizing the calcine reactant in the elongate rotary calcination kiln with a burner
disposed at a burner end of the elongate rotary calcination kiln, the burner end being distally
disposed form the feed end; and
introducing NCGs into the elongate rotary calcination kiln, through a plenum chamber
annularly disposed around a tubular housing of the elongate rotary calcination kiln, wherein the
plenum chamber fluidly communicates with a kiln chamber through an opening, and wherein a
temperature of the kiln chamber is in a range of 1,300 °F to 1,750 °F (704°C to 954°C) at an
insertion location.
The problems of mid-kiln ring formation in an elongate rotary calcination kiln, such as
a lime kiln, due to temperature fluctuations at the burner end and NOx emissions resulting from
combustion of nitrogen and oxygen compounds in the elongate rotary calcination kiln are mitigated
by introducing non-condensable gases (“NCGs”) into the elongate rotary calcination kiln, at an
insertion location, wherein a temperature at the insertion location is in a range of 212 degrees
Fahrenheit (“°F”) to 2,200 °F (100 degrees Celsius (“°C”) to about 1,204.44 °C). Desirably, the
NCGs are not inserted into a burner end of the elongate rotary calcination kiln. The insertion
location is desirably in a “pre-heating zone” or in a separate “calcining zone”. In another
exemplary embodiment, the temperature at the insertion location may be in the range of 1,300 °F
to about 1,750 °F (760 °C to about 954 °C). In other exemplary embodiments, the temperature at
the insertion location may be below 1,300 °F to reduce thermal NO further while still oxidizing
the NCGs.
For reference, the elongate rotary calcination kiln comprises a kiln chamber having a
burner end distally disposed from a feed end. The calcining zone begins at the burner end and may
extend about 30% to about 40% the length of the elongate rotary calcination kiln. The calcining
zone may have a temperature range of about 1,300 °F to about 2,200 °F. The pre-heating zone of
the elongate rotary calcination kiln is disposed downstream of the calcining zone relative to the
burner end. The pre-heating zone may have a temperature range of about 212 °F to about 1,300
°F (100 °C to about 760 °C).
Without being bounded by theory, Applicant has discovered that by inserting NCGs
into the elongate rotary calcination kiln downstream of the burner end at an insertion location
having a temperature of about 212 °F to about 2,200 °F (preferably 1,300 °F to about 2,200 °F)
that such a method reduces sporadic flame activity in the burner end, which in turn may reduce the
freeze-thaw cycles that allow mid-kiln rings to grown from the refractory material toward the axis
of the calcination kiln rotation. Injecting NCGs at such an insertion location may further allow
the NCGs to mix with kiln gases and lower the temperature near the insertion location and
downstream of the insertion location to thereby reduce NO generation.
The exemplary method and system disclosed herein may further allow more precise
temperature regulation within the calcination kiln chamber.
An exemplary elongate rotary calcination kiln system may comprise: a tubular housing
having an outer shell and a refractory lining disposed within the outer shell. The refractory lining
defines a kiln chamber; the kiln chamber has a burner end, a feed end distally disposed from the
burner end, and a length extending between the burner end and the feed end. The exemplary
system may further have a plenum annularly disposed around the tubular housing. The plenum
may comprise a plenum housing. The plenum housing defines a plenum chamber annularly
disposed around the tubular housing, and the plenum chamber fluidly communicates with the kiln
chamber through an opening. The opening into the kiln chamber is disposed at about two-thirds
the length of the kiln chamber as measured from the burner end at an insertion location where the
kiln chamber temperature is in a range of 1,300 °F to 1,750 °F, or 1,400 °F to 1,750 °F, or 1,500
°F to 1,750 °F. In this way, the plenum is configured to convey the NCGs into the pre-heating
zone or calcining zone of the kiln chamber.
An exemplary process for reducing the accumulation of mid-kiln rings in an elongate
rotary calcination kiln, particularly a lime kiln, may comprise: introducing NCGs into a chamber
of a rotary lime kiln, through a plenum chamber annularly disposed around a tubular housing of
the lime kiln. In the exemplary process, the plenum chamber fluidly communicates with the kiln
chamber at an opening. The temperature of the kiln chamber can be in a range of 1,300° F to
1,750° F at the opening.
In still other exemplary embodiments, operators may add ammonia (NH ) or urea
(CH N O) downstream of the burner end to mitigate nitrous oxide (“NO ”) emissions.
4 2 X
It is contemplated that certain exemplary embodiments may allow mill owners to
retrofit existing elongate rotary calcination kilns with the system described more fully herein.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing will be apparent from the following more particular description of
exemplary embodiments of the disclosure, as illustrated in the accompanying drawings in which
like reference characters refer to the same parts throughout the different views. The drawings are
not necessarily to scale, with emphasis instead being placed upon illustrating the disclosed
embodiments.
is a cross-sectional schematic diagram of an exemplary elongate rotary
calcination kiln comprising a plenum chamber disposed about two-thirds down the length of the
calcining kiln chamber as measured from the burner end.
is a side view of an exemplary elongate rotary calcination kiln showing a
plenum chamber disposed at about two thirds the length of the calcining kiln chamber as measured
form the burner end.
is a perspective view of the plenum section of the exemplary system having a
quarter cutaway depicting the manner in which the plenum chamber fluidly communicates with
the calcining kiln chamber.
is a side cross-sectional view of the plenum section of the exemplary system
showing the insertion of non-condensable gases (“NCGs”) downstream of the burner through the
plenum.
is a cross-sectional schematic view of an exemplary elongate rotary calcination
kiln system wherein the elongate rotary calcination kiln is a flash dryer kiln.
is a cross-sectional schematic diagram depicting an exemplary method for
reducing mid-kiln ring formation and an exemplary system further comprising a thermocouple.
DETAILED DESCRIPTION OF THE INVENTION
The following detailed description of the preferred embodiments is presented only for
illustrative and descriptive purposes and is not intended to be exhaustive or to limit the scope and
spirit of the invention. The embodiments were selected and described to best explain the principles
of the invention and its practical application. One of ordinary skill in the art will recognize that
many variations can be made to the invention disclosed in this specification without departing from
the scope and spirit of the invention.
Corresponding reference characters indicate corresponding parts throughout the several
views. Although the drawings represent embodiments of various features and components
according to the present disclosure, the drawings are not necessarily to scale and certain features
may be exaggerated in order to better illustrate embodiments of the present disclosure, and such
exemplifications are not to be construed as limiting the scope of the present disclosure in any
manner.
References in the specification to “one embodiment”, “an embodiment”, “an exemplary
embodiment”, etc., indicate that the embodiment described may include a particular feature,
structure, or characteristic, but every embodiment may not necessarily include the particular
feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the
same embodiment. Further, when a particular feature, structure, or characteristic is described in
connection with an embodiment, it is submitted that it is within the knowledge of one skilled in
the art to affect such feature, structure, or characteristic in connection with other embodiments
whether or not explicitly described.
Although specific terms are used in the following description for the sake of clarity,
these terms are intended to refer only to the particular structure of the embodiment selected for
illustration in the drawings, and are not intended to define or limit the scope of the disclosure.
The singular forms “a,” “an,” and “the” include plural referents unless the context
clearly dictates otherwise. Numerical values should be understood to include numerical values
which are the same when reduced to the same number of significant figures and numerical values
which differ from the states value by less than the experimental error of conventional measurement
technique of the type described in the present application to determine the value.
All ranges disclosed herein are inclusive of the recited endpoint and are independently
combinable (for example, the range “from 2 grams to 10 grams” is inclusive of the endpoints, 2
grams and 10 grams, and all intermediate values.
As used herein, approximating language may be applied to modify any quantitative
representation that may vary without resulting in a change in the basic function to which it is
related. Accordingly, a value modified by a term or terms, such as “about” and “substantially,”
may not be limited to the precise values specified. The modifier “about” should also be considered
as disclosing the range defined by the absolute values of the two endpoints. For example, the
expression “from about 212 °F to about 1,300 °F” also discloses the range “from 212 °F to 1,300
°F.”
It should be noted that many of the terms used herein are relative terms. For example,
the terms “upper” and “lower” are relative to each other in location, i.e. an upper component is
located at a higher elevation than a lower component in a given orientation, but these terms can
change if the device is flipped. The terms “inlet’ and “outlet” are relative to a fluid flowing through
them with respect to a given structure, e.g. a fluid flows through the inlet into the structure and
flows through the outlet out of the structure. The terms “upstream” and “downstream” are relative
to the direction in which a fluid flows through various components, i.e. the flow of fluids through
an upstream component prior to flowing through the downstream component.
The terms “horizontal” and “vertical” are used to indicate direction relative to an
absolute reference, i.e. ground level. However, these terms should not be construed to require
structure to be absolutely parallel or absolutely perpendicular to each other. For example, a first
vertical structure and a second vertical structure are not necessarily parallel to each other. The
terms “top” and “bottom” or “base” are used to refer to locations/surfaces where the top is always
higher than the bottom/base relative to an absolute reference, i.e. the surface of the Earth. The
terms “upwards” and “downwards” are also relative to an absolute reference; an upwards flow is
always against the gravity of the Earth.
The term “directly,” wherein used to refer to two system components, such as valves
or pumps, or other control devices, or sensors (e.g. temperature or pressure), may be located in the
path between the two named components.
is a cross-sectional schematic diagram of an elongate rotary calcination kiln
100. The elongate rotary calcination kiln 100 may be used to calcine lime, cement, magnesia,
dolomite, titanium dioxide, and other calcined compounds. The elongate rotary calcination kiln
100 comprises a tubular housing 102. The tubular housing 102 is generally inclined at an angle of
about 2° to about 5° from a horizontal line H. The tubular housing 102 can have an outer shell
103, usually fabricated from steel, and a refractory lining 107. The refractory lining 107 commonly
comprises bricks, concrete, ceramics, or other materials that retain strength at kiln temperatures.
The refractory lining 107 defines a kiln chamber 115. The kiln chamber 115 has a burner end 105
and a feed end 110 distally disposed from the burner end 105. The burner end 105 may be disposed
in a kiln hood 116. The feed end 110 is sometimes known as the “cold end” and the burner end
105 is sometimes referred to as the “hot end” by those having ordinary skill in the art. A length L
separates the burner end 105 from the feed end 110. Elongate rotary calcination kilns 100 can
vary in size, but a typical elongate rotary calcination kiln 100 may be between about 200 feet to
about 400 feet in length L.
The elongate rotary calcination kiln 100 further comprises a drive gear 113 and multiple
riding rings 117 annularly engaged to the tubular housing 102. The riding rings 117 rest on rollers
(326, disposed on support blocks (247, . In operation, a motor (not depicted)
rotates the drive gear 113 and thereby rotates the riding rings 117 and the elongate rotary
calcination kiln 100 around a center rotational axis C. The elongate rotary calcination kiln 100
typically rotates at about one to two revolutions per minute. A burner 124 is disposed at the burner
end 105 of the kiln chamber 115. In operation, the burner 124 emits a flame jet 122 to heat the
kiln chamber 115. Because the burner 124 is disposed only at the burner end 105, the burner
distributes heat unevenly along the length L of the kiln chamber 115. This uneven heat distribution
creates several temperature zones 172, 174, 176.
Operators may refer to the temperature zone starting at the feed end 110 as a “drying
zone” 172. In the drying zone 172, heat from the flue gases 125 evaporates excess moisture in the
calcine reactants 120 (i.e. lime mud when the elongate rotary calcination kiln 100 is a lime kiln).
Because the drying zone 172 is configured to evaporate excess moisture, the lower end of drying
zone’s effective temperature range is typically the boiling point of water, i.e. 212 degrees
Fahrenheit (°F) or 100 degrees Celsius (°C). A typical drying zone 172 may extend about 20% to
about 30% of the length L of the elongate rotary calcination kiln 100 as measured from the feed
end 110.
A preheating zone 174 is typically disposed between the drying zone 172 and the
calcining zone 176. The preheating zone 174 typically has a temperature range of between 212 °F
and 1,300 °F (100 °C and 760 °C). Flue gases 125 heat the calcine reactants 120 in the preheating
zone 174 and begin to form the calcine reactants 120 into larger nodules 120’ (e.g. lime nodules).
Generally, elongate rotary calcination kilns 100 process nodules 120’ ranging in size from about
1 millimeter (mm) to about 50 mm. A typical preheating zone 174 may extend about 30% to about
40% of the length L of the elongate rotary calcination kiln 100 between the drying zone 172 and
the calcining zone 176.
The calcining reaction primarily occurs in the calcining zone 176. The calcining zone
176 typically extends about 30% to about 40% the length L of the elongate rotary calcination kiln
100 as measured from the burner end 105. The calcining zone 176 typically has a temperature
range of about 1,300 °F and 2,200 °F (760 °C and 1,204.44 °C).
It will be understood by persons having ordinary skill in the art that the temperature
zones 172, 174, 176 are presented for illustrative purposes and that the positions of the
temperatures zones 172, 174, 176 may fluctuate over time given the burner output. However, the
range of temperatures comprising each temperature zone 172, 174, 176 permits the location of
each zone to be ascertained in operation. The lines depicted in are included for elucidating
the approximate locations of the temperature zones 172, 174, 176.
Natural gas or oil typically serve as primary burner fuels. However, to conserve the
amount of available primary fuel and reduce costs, operators typically supplement the primary fuel
with one or more auxiliary fuels 129. Some of these auxiliary fuels 129 are byproducts of pulp
and paper production and chemical recovery of white liquor. Others auxiliary fuels 129 are used
because the auxiliary fuels 129 are either inexpensive or readily available. Collectively, these
auxiliary fuels 129 can include hazardous air pollutants (“HAPs”) such as liquid methanol and
turpentine. Furthermore, auxiliary fuels 129 may include hydrogen, tall oil, glycerol, low-volume,
high concentration non-condensable gases (“LVHC NCGs,” also known as “concentrated NCGs”
or “CNCGs”) produced from a pulp mill, stripper off gases (“SOG”, another type of NCG)
produced from an evaporation plant, petroleum coke, gasification gas (typically from biofuel such
as bark, wood, etc.) biogas (typically methane and inert gases), gasification gas from coal, and
liquid natural gas. It will be understood the auxiliary fuels 129 may include combinations of fuels.
Operators feed the auxiliary fuels 129 directly to the burner 124 or insert the auxiliary
fuels 129 close to the flame jet 122 so that the auxiliary fuels 129 will combust near the burner end
105.
The burning of fuels creates “fuel NO ” formed from the oxidation of already-ionized
nitrogen in the primary and auxiliary burner fuels 129. “Thermal NO ” describes NO created
through the combustion of nitrogen and oxygen compounds in a system.
Additionally, operators may feed low-concentration high volume non-condensable
gases (“LCHV NCGs,” also known as “dilute NCGs” or “DNCGs”) 166 close to the flame jet 122
to oxidize these LCHV NCGs 166 prior to exiting the feed end 110 of the elongate rotary
calcination kiln 100. The oxidation process reduces the amount of pollutants exiting the elongate
rotary calcination kiln 100. Operators also burn low volume high concentration (“LVHC”) gases
in the kiln. These LVHC gases contain much higher concentrations of sulfur gases as well as
vaporized methanol. LCHV NCGs typically contain only 5% to 6% NCG’s by volume. These
LCHV NCG’s 166 typically comprise total reduced sulfur (“TRS”) gases produced in the cooking
and black liquor concentration processes. These TRS gases may include for example, sulfur
compounds such as hydrogen sulfide (H S), methanethiol (CH S), dimethyl disulfide ((CH ) S ),
2 4 3 2 2
and dimethyl sulfide, ((CH ) S). TRS gases are corrosive and should not be used with carbon
steel. NCGs are also highly toxic. TRS gases and the common HAPs methanol, and turpentine
that may be present with NCGs, can explode in the presence of sufficient oxygen.
Generally, the calcine reactant 120 (e.g. lime mud in pulp and paper chemical recovery)
enters the feed end 110 of the kiln chamber 115 and flow downwards toward the burner end 105.
The calcine reactants 120 flow counter to the flow of flue gases 125. The flue gases 125 eventually
exit the feed end 110 as exhaust gases 133. At the burner end 105, the re-burned product 127 (e.g.
lime) exits the elongate rotary calcination kiln 100 at about 1,750°F (954.44 °C). To reclaim some
of the heat in the elongate rotary calcination kiln 100, many elongate rotary calcination kilns 100
have coolers 138 proximate to the burner end 105. The cooler 138 may collect cool air 128 from
the atmosphere and pass this cool air 128 over the exiting re-burned product 127. The hot re-
burned product 127 pre-heats this cool air 128 before this secondary cool air 128 enters the kiln
chamber 115 to maintain combustion.
When the elongate rotary calcination kiln 100 is a lime kiln, the calcine reactant 120 is
lime mud. The lime mud typically has a moisture concentration of between 20% and 30% at the
feed end 110. As the lime mud (see 120) flows toward the burner end 105, residual heat in the
flue gases 125 evaporates the remaining moisture and preheats the lime mud (see 120). The
calcining reaction begins when the lime mud temperature reaches 1,400°F, but the reaction
proceeds well only after the lime mud (see 120) reaches 1,800°F. To transfer heat from the flue
gases 125 to the lime mud (see 120) more efficiently, elongate rotary calcination kilns 100 typically
have a chain section 118. The multiple chains 121 increase the surface area within the kiln
chamber 115 exposed to the flue gases 125 and therefore increase the efficiency with which the
heat from the flue gases 125 transfers to the lime mud (see 120).
As kiln chamber temperatures approach calcination temperatures of about 1,400°F to
over 1,800 °F, the lime mud (see 120) plasticizes and pelletizes. When the calcine reactant 120 is
lime mud, the calcining reaction generally proceeds as follows: CaCO + heat ↔ CaO + CO . The
completeness of the calcining reaction is a function of the retention time and the temperature
profile of the elongate rotary calcination kiln 100.
However, in practice, some of the pelletized lime mud (CaCO ) (see 120) accumulates
into larger nodules 120’. Over time, the lime dust adheres to and coats the refractory lining 107.
As more lime dust accumulates on the refractory lining 107 and as the elongate rotary calcination
kiln 100 continues to rotate, the lime mud (see 120) adhering to the refractory lining 107 forms a
mid-kiln ring 130. Initially, a mid-kiln ring 130 is believed to contain both quick lime, (CaO) and
lime mud (CaCO ). This process can also create soda balls ranging in size from about 0.5 feet to
about 2 feet. These soda balls are undesirable in part because the soda balls prevent the calcination
reaction from proceeding efficiently.
Ring formation (see 130) increases precipitously between 150 feet and 200 feet when
the flue gases have temperatures ranging from about 1,800 °F to about 1,700 °F and the
temperature of the solid materials range from about 1,500 °F to about 1,150 °F. Without being
bounded by theory, it is believed the when the lime mud (see 120) reaches calcining temperatures
in the preheating zone 174 and calcining zone 176, sodium compounds vaporize from the calcine
reactant bed 123. Some of the sodium will condense on the sodium itself, thereby making a fume
particle. Some of the sodium will stick to the lime. The molten sodium is believed to act as a
“glue” that can attract further lime particles to stick together and to the refractory lining 107 of the
elongate rotary calcination kiln 100. This sodium can combine with a CO anion. Re-carbonation
and sulfation reactions will harden the agglomeration of lime being held together by the alkali
“glue”. Temperature fluctuations within the kiln chamber 115 create cycles of freezing and
thawing. These freezing and thawing cycles deposit new overlapping layers of material in the
same basic area, thereby gradually creating a large, structurally stronger ring formation. When the
rate of erosion no longer equals the rate of deposition, the mid-kiln ring 130 grows and effectively
reduces the diameter of the kiln chamber 115.
In a lime kiln (see 100), the size of the mid-kiln ring 130 was typically thought to be
heavily dependent upon the lime mud’s (see 120) sodium content. If operators do not periodically
deactivate the elongate rotary calcination kiln 100 to remove these rings, the growing mid-kiln
ring 130 eventually obstructs the kiln chamber 115, thereby rendering the elongate rotary
calcination kiln 100 unusable without extended shutdown and maintenance.
is a side view of an exemplary elongate rotary calcination kiln 200 comprising
a plenum 250 disposed about two-thirds the length L of the kiln chamber 115 from the burner end
205. The plenum 250 may be disposed annularly around the tubular housing 202 at the preheating
zone 274 or calcining zone 276. Without being bounded by theory, it is believed that full oxidation
of the NCGs can still occur in the preheating zone 274. In other exemplary embodiments, the
plenum 250 may be disposed upstream of the drive gear 213. The kiln chamber 115 and tubular
housing 202 may expand uphill and downhill from the drive gear 213. It may therefore be desirable
to place the plenum 250 proximate to the drive gear 213, or to at least avoid areas of tubular
housing 202 expansion to avoid inconsistent fittings between the plenum 250 and tubular housing
202 and possible deformations in the seal 357 ( connecting the plenum chamber 250 to the
tubular housing 202.
In an exemplary process, operators feed NCGs 265 through an inlet conduit 262 leading
to the plenum 250. Unless further specified, NCGs 265 may refer to LCHV NCGs, LVHC NCGs,
SOGs, chip bin gases (“CBG”) or combinations thereof. Without being bounded by theory, it may
be desirable to insert primarily LCHV NCGs into the preheating zone 274 or the calcining zone
276. LCHV NCGs comprise about 5% to about 6% NCGs by volume. The remaining
concentration is typically air. By inserting the LCHV NCGs at an insertion location (375,
where the temperature is lower than the temperature at or near the burner end 205, the exemplary
system not only introduces the NCGs 265 at an area of reduced temperature, but the NCGs
themselves, particularly LCHV NCGs may further reduce the temperature of the chamber 215 at
or near the insertion location 375. This temperature reduction may disrupt the stoichiometric ratio
that is conducive to NO formation. That is, the injection of NCGs 265 into the pre-heating zone
274 or calcining zone 276 downstream of the burner end 205 may disrupt the exact ratio of nitrogen
and oxygen compounds available to form NO in part through diluting the calories available to
react these nitrogen and oxygen compounds to form NO . Furthermore, by inserting the NCGs
265 downstream of the burner end 205, the exemplary system and process disclosed herein may
further reduce the residence time of any NOx-forming compounds present in, or injected with the
NCGs 265, thereby further reducing the NO capable of being created in the system. Furthermore,
by oxidizing the NCGs 265 downstream of the burner end 205 rather than combusting the NCGs
265 in the burner flame 122, the exemplary systems and processes disclosed herein prevent a
further source combustion necessary to create thermal NO thereby contributing to an overall NO
reduction. NCGs collected from pulp mill processes are typically at a temperature of about 140
°F (60 °C) or cooler in transportation conduits. In certain exemplary embodiments, the collected
NCGs 265 may feed directly into the kiln chamber 315 as the NCGs 265 are received from the
mill sources (e.g. chemical digesters, chip bins, evaporators, and turpentine systems). In other
exemplary embodiments, the NCGs 265 may be cooled to below 140 °F (60 °C) prior to being
inserted into the kiln chamber (315, . In still other exemplary embodiments, the NCGs 265
may be heated to approximately the temperature of the kiln chamber 315 at the insertion location
375. For comparison, recirculated flue gas is generally in the range of 500 °F (260 °C) to 1,400
°F (760 °C) depending on where the flue gas is recirculated. In Andritz kilns for example, the
recirculated flue gas generally has a temperature of between about 500 °F (260 °C) and 650 °F
(about 343 °C).
is a perspective close-up view of the plenum 350 of an exemplary elongate
rotary calcination kiln 300 disposed around the tubular housing 303. shows a cutaway
depicting the inside of the plenum 350 and the kiln chamber 315. The plenum 350 is annularly
disposed around the elongate rotary calcination kiln 300 at about two thirds the length L of the
kiln chamber 315 as measured from the burner end 205. The plenum 350 comprises a plenum
housing 351. The plenum housing 351 defines a plenum chamber 353 annularly disposed around
the outer shell 303 of the tubular housing 302. Seals 357 isolate the plenum chamber 353 from
the outside atmosphere and allow the elongate rotary calcination kiln 300 to rotate while the
plenum 350 remains stationary. Legs 354 may support the plenum 350 on the support block 347.
The plenum chamber 353 communicates with an inlet conduit 362 at a plenum inlet
363 defined by the plenum housing 351. The plenum chamber 353 further communicates with the
kiln chamber 315 through one or more openings 368 in the tubular housing 302. A gas conduit
364 may extend through the opening 368. In other exemplary embodiments, the gas conduit 364
may be omitted. In operation, operators direct NCGs 365, preferably LVHC NCGs including total
reduced sulfur (“TRS”) gases, through the inlet conduit 362 into the plenum chamber 353. From
the plenum chamber 353, the NCGs365 diffuse into the kiln chamber 315 through the openings
368 and if present, the gas conduits 354. The NCG’s 365 may enter the kiln chamber 315 at the
preheating zone 274 or the calcining zone 276.
During operation, a temperature T at the insertion location 375 at which the NCGs 365
enter the kiln chamber 315 is between about 1,300 °F to 1,750 °F. depicts multiple
openings 368 in the tubular housing 302 with a gas conduit 364 extending through each opening
368. In the depicted embodiment, it will be understood that that insertion location 375 is disposed
at the kiln chamber end of the gas conduit 364. In exemplary embodiments lacking gas conduits
364, the insertion location 375 is just inside the kiln chamber 315 relative to the opening 368. It
will be understood that in other exemplary embodiments, more than one plenum 350 may be
disposed along the length L of the elongate rotary calcination kiln 300 provided that the additional
plenums 350 are configured to introduce NCGs 356 at insertion locations 375 in the kiln chamber
having a temperature T of about 212 °F to about 2,200 °F and preferably between about 1,300 °F
and 1,750 °F. Other structures suitable for injecting NCGs 365 into an elongate rotary calcination
kiln 300 as described herein are considered to be within the scope of this disclosure.
is a cross-sectional side view of the plenum section of an exemplary elongate
rotary calcination kiln 400 shown in Without being bounded by theory, Applicant has
discovered that the variable composition of the TRS gases in the NCGs 465 causes temperature
variations in the kiln chamber 415, which can disrupt the flame 122. The flow of NCGs 465 into
the burner end 105 may cool the burner end 105 and thereby contribute to temperature fluctuations
throughout the kiln chamber 415. Oxidizing NCGs 166 at the burner end (as shown in
may displace the oxygen that the burner 124 requires to maintain the flame 122. Without sufficient
oxygen, the flame 122 will starve and contribute to “blowback”. Blowback occurs when a
diminished flame 122 ignites built-up pockets of combustible fuel. The sudden ignition of the
built-up fuel can produce a small explosion that can render the elongate rotary calcination kiln 100
unsafe to nearby operators and contribute significantly to temperature fluctuations within the kiln
chamber 415.
Applicant has discovered that by inserting the NCGs 465 into to pre-heating zone 274
or into the calcining zone 276, the temperatures of the pre-heating zone 274 and calcining zone
276 are sufficient to oxidize the NCGs 465 prior to the NCGs 465 exiting the feed end 210 of the
elongate rotary calcination kiln 200, while moving the cooling effects of the NCGs 465
downstream of the middle of the elongate rotary calcination kiln 200 (relative to the burner end
205), and thereby bypassing the area of the elongate rotary calcination kiln 200 in which mid-kiln
rings 130 are likely to form. By inserting NCGs 465 into a plenum 450 disposed about one half
(½) to two thirds (⅔) the length L of the elongate rotary calcination kiln 200, Applicant has
discovered a way to reduce temperature fluctuations at the burner end 205 and thereby bypass the
freezing and thawing cycles that contributed to the creation of mid-kiln rings 130. With reduced
temperature fluctuations, the nodules 120’ are less likely to accumulate additional material at a
faster rate than which the nodules 120’ lose material, thereby obviating the opportunity for mid-
kiln rings 130 to form.
Inserting the NCGs 465 into the pre-heating zone 274 may further cool the flue gases
125 downstream of the pre-heating zone 274 (e.g. in the drying zone 272), thereby passively
keeping the drying zone 272 below 1,300 °F and avoiding the accumulation of lime mud dust
(CaCO ) adhering to the refractory walls 407 into mid-kiln rings 130. The accumulation of lime
mud on the refractory walls 107 due to successive freeze and thaw cycles is believed to be the
impetus of mid-kiln ring 130 formation. The exemplary system thereby prevents the formation of
mid-kiln rings 130 in the pre-heating zone 274. The elongate rotary calcination kiln 400 is less
likely to produce NO at temperatures below 1,400 °F.
In another exemplary embodiment, operators may add air (A, to the plenum
450 in addition to NCG s 465. It is believed that the addition of air A can help control the
temperature ranges within the elongate rotary calcination kiln 400 and further mitigate ringing and
NO production, particularly thermal NO production.
In yet another exemplary embodiment, operators may inject urea (CH N O) into the
plenum 450 to reduce the accumulation of nitrous oxides (NO ) in the exhaust gases 633. (See
FIGs. 5 and 77). In yet another exemplary embodiment, operators may inject ammonia (NH ) into
the plenum 450 to reduce the accumulation of nitrous oxides (NO ) in the exhaust gases 633. (See
FIGs. 5 and 6).
is a cross-sectional schematic view of an exemplary elongate rotary calcination
kiln system wherein the elongate rotary calcination kiln 200 is a flash dryer kiln 500. In a flash
dryer kiln 500, a flash dryer 570 replaces the chain section 118 present in standard elongate rotary
calcination kilns 100. The flash dryer 570 is typically disposed above the feed end 510. The flash
dryer 570 replaces the drying zone 272 in the standard elongate rotary calcination kilns 100. The
burner 524 and tubular housing 502 therefore define the calcining zone 576 and a preheating zone
574 in the kiln chamber 515 of the tubular housing 502.
Prior to entering the flash dryer 570, operators typically dewater the calcine reactant
520 in a lime filter (not depicted). In the calcine reactant is lime mud. The dewatered
lime mud (see 520) will generally have a moisture content in a range of 20% to 30% when entering
the flash dryer 570. In a flash drying process, operators feed lime mud (see 520) into the flash
dryer 570 at an inlet 571. The lime mud (see 520) then briefly encounters exhaust gases 533
captured from the feed end 510 of the kiln chamber 515. The exhaust gases may exit the feed end
510 of the kiln chamber 515 in excess of 1292 °F (700 °C). The hot exhaust gases 533 rapidly
evaporate excess moisture in the lime mud (see 520) without heating the lime mud (see 520) long
enough to catalyze the calcining reaction. In this manner, the flash dryer 570 dries the lime mud
520”. A cyclone separator 573 separates the dried lime mud 520” from the exhaust gases 533.
The separated dried lime mud 520” is then fed into the feed end 510 of the elongate rotary
calcination kiln 200 for preheating and calcination.
depicts a plenum 550 disposed around the tubular housing 502 near the drive
gear 513. The plenum 550 is disposed at an insertion location 575, wherein a temperature T of the
kiln chamber 515 is in a range of 1,300° F to 1,750° F at the insertion location 575. Operators
feed NCGs 565 into the plenum 550 at the insertion location 575 to reduce temperature fluctuations
at the burner end 505 to thereby avoid the cyclic freezing and thawing of lime accumulations that
contribute to the creation of mid-kiln rings 130.
Reduced temperature fluctuations in the kiln chamber 515, particularly in the calcining
zone 576 and preheating zone 574 may permit the burner 524 and flame 522 to heat the kiln
chamber 515 consistently thereby improving the throughput of calcine reactants 520 and the
consistency of the re-burned product 527.
is a cross-sectional schematic representation of a process for reducing the
accumulation of mid-kiln rings (see 130) in an elongate rotary calcination kiln 600 comprising:
introducing NCGs 665 into a elongate rotary calcination kiln 600, at an insertion location 675,
wherein a temperature T of the kiln chamber 615 is in a range of 1,300° F to 1,750° F at the
insertion location 675, wherein the NCGs 665 are desirably not inserted into a burner end 605 of
the elongate rotary calcination kiln 600. The insertion location 675 is desirably in the pre-heating
zone 674 or the calcining zone 676.
In certain exemplary embodiments, operators may inject ammonia (NH ) into the kiln
chamber 615 at the insertion location 675 to reduce the accumulation of nitrous oxides (NO ) in
the exhaust gases 633 through selective catalytic reduction (“SCR”). In still other exemplary
embodiments, operators may inject urea (CH N O) and ammonia (NH ) into the kiln chamber 615
4 2 3
at the insertion location 675 to reduce the accumulation of nitrous oxides (NO ) in the exhaust
gases 633 through selective non-catalytic reduction (“SNCR”). In yet another exemplary
embodiments, operators may add steam or water vapor (H O) at the insertion location 675 to help
regulate the internal temperature and to help maintain the insertion locations of the temperature
zones 672, 674, 676. It is contemplated that the emissions of sulfur oxides (“SO ”) may remain
substantially unchanged.
In still other exemplary embodiments, operators may add sintering agents S with the
NCGs 665 to reduce mid-kiln ring 130 formation further and to facilitate more frequent spalling
of contaminants from the refractory walls 607. In yet other exemplary embodiments, operators
may add oxygen (O ) with the NCGs 665 to facilitate oxidation of the NCGs 665 near the insertion
location 675. In still other exemplary embodiments, operators may insert air A with the NCGs
665 at the insertion location 675 to facilitate oxidation of the NCGs 665. In yet further exemplary
embodiments, operators may recirculate flue gas FG at the insertion location 675. The flue gas
FG may be cooled prior to insertion. In other exemplary embodiments, the flue gas FG may be
oxygen-depleted. Without being bounded by theory, it is contemplated that the addition of flue
gas FG, air A, water vapor (H O), or any combination thereof may dilute combustion energy
needed to create NO . Water vapor (H O), water, cooled flue gas FG, and air A may be referred
to generically as “cooling agents” 679 in this disclosure.
also schematically depicts and exemplary system comprising an elongate rotary
calcination kiln 600 having a burner end 605 distally disposed from a feed end 610. The elongate
rotary calcination kiln 600 comprises an outer shell 603, and a refractory lining 607. The refractory
lining 607 defines a kiln chamber 615 comprising multiple temperature zones 672, 674, 676. The
exemplary system further comprises a temperature sensor 695 such as a thermocouple. The
temperature sensor 695 detects the temperature T of kiln chamber 615 near the location of the
temperature sensor 695. depicts a first temperature sensor 695a and disposed upstream of
the insertion location 675 (i.e. closer to the burner end 605) and a second temperature sensor 695b
disposed downstream of the insertion location 675 (i.e. closer to the feed end 610). The
temperature sensor 695 may signally communicate with a programmable logic controller (“PLC”),
computer, tablet computer, or smart phone (generically, “processor”). The processors may send
an output signal to a display to allow an operator to see or otherwise visualize the temperature
readings.
An operator may adjust a process condition based on a reading from the temperature
sensor 695 to maintain desirable operating conditions. In other exemplary embodiments, the
processor may adjust a process condition automatically based upon readings from the temperature
sensor 695. For example, if the temperature sensor 695 indicates that the temperature of the pre-
treatment zone 674 is falling below desirable levels, the operator may increase the amount of fuel
consumed by the burner 624 to increase the length of the flame 622 and thereby return the an area
of the kiln chamber 615 to a desirable temperature T.
A further process for reducing the accumulation of kiln rings in an elongate rotary
calcination kiln 600 may comprise: feeding a calcine reactant 620 into an elongate rotary
calcination kiln 600 at a feed end 610 of the elongate rotary calcination kiln 600, oxidizing the
calcine reactant 620 in the elongate rotary calcination kiln 600 with a burner 624 disposed at a
burner end 605 of the elongate rotary calcination kiln 600, the burner end 605 being distally
disposed form the feed end 610; and introducing NCGs 665 into the elongate rotary calcination
kiln 600, through a plenum chamber 453, 553 annularly disposed around a tubular housing 602 of
the elongate rotary calcination kiln 600, wherein the plenum chamber 453, 553 fluidly
communicates with a kiln chamber 615 through an opening 668, and wherein a temperature T of
the kiln chamber 615 is in a range of 1,300 °F to 1,750 °F at an insertion location 675.
Another exemplary process comprises: measuring a first temperature T at a first
location upstream of the insertion location 675, measuring a second temperature T at a second
location downstream of the insertion location 675, comparing the first temperature T to the second
temperature T to determine the temperature difference, adding a cooling agent 679 with the NCGs
665 at an insertion location 675 when the temperature difference is less than 100 °F, wherein the
temperature T at the insertion location 675 is between 212 °F and 2,200 °F. In other exemplary
embodiments, the temperature T at the insertion location is between 1,300 °F and 1,750 °F. An
exemplary method may further comprise ceasing to add a cooling agent 679 when the temperature
difference is 100 °F or greater. In still other exemplary embodiments, operators may add cooling
agent 679 when the temperature difference reaches 100 °F.
While this invention has been particularly shown and described with references to
exemplary embodiments thereof, it will be understood by those skilled in the art that various
changes in form and details may be made therein without departing from the scope of the invention
encompassed by the appended claims.
In the present specification and claims (if any), the word ‘comprising’ and its
derivatives including ‘comprises’ and ‘comprise’ include each of the stated integers but does not
exclude the inclusion of one or more further integers.
Reference throughout this specification to ‘one embodiment’ or ‘an embodiment’
means that a particular feature, structure, or characteristic described in connection with the
embodiment is included in at least one embodiment of the present invention. Thus, the
appearance of the phrases ‘in one embodiment’ or ‘in an embodiment’ in various places
throughout this specification are not necessarily all referring to the same embodiment.
Furthermore, the particular features, structures, or characteristics may be combined in any
suitable manner in one or more combinations.
In compliance with the statute, the invention has been described in language more or
less specific to structural or methodical features. It is to be understood that the invention is not
limited to specific features shown or described since the means herein described comprises
preferred forms of putting the invention into effect. The invention is, therefore, claimed in any
of its forms or modifications within the proper scope of the appended claims (if any)
appropriately interpreted by those skilled in the art.
Claims (20)
1. An elongate rotary calcination kiln system comprising: a tubular housing having an outer shell and a refractory lining disposed within the outer shell, the refractory lining defining a kiln chamber, the kiln chamber having a burner end, a feed end distally disposed from the burner end, and a length extending between the burner end and the feed end; a plenum annularly disposed around the tubular housing, the plenum comprising a plenum housing defining a plenum chamber annularly disposed around the tubular housing, wherein the plenum chamber fluidly communicates with the chamber through an opening disposed at an insertion location, at about two thirds the length of the kiln chamber as measured from the burner end, wherein the plenum is configured to convey NCGs into the kiln chamber through the opening at the insertion location, and wherein a temperature at the insertion location is between 212 °F and 2,200 °F (100°C and about 1,204.44 °C).
2. The system of claim 1, wherein the insertion location is at a pre-heating zone of the kiln chamber, wherein the temperature at the insertion location is between 212 °F and 1,300 °F (100°C and 704°C).
3. The system of claim 2, further comprising a calcining zone extending from the burner zone to about 30% of the length of the chamber as measured from the burner end, wherein the pre-heating zone is disposed downstream of the calcining zone and extends about 30% to about 40% the length of the kiln chamber as measured from the burner end.
4. The system of claim 1, wherein the insertion location is at a calcining zone of the kiln chamber, wherein the calcining zone is disposed about 30% to about 40% the length of the kiln chamber as measured from the burner end, and wherein the temperature at the insertion location is between 1,300 °F and 2,200 °F (between 100°C and about 1,204.44 °C).
5. The system of claim 1 further comprising a drying zone disposed about 30% of the length of the elongate rotary calcination kiln starting at the feed end.
6. The system of claim 1 further comprising a temperature sensor disposed proximate to the insertion location.
7. The system of claim 1, wherein the temperature at the insertion location is between 1,300 °F and 1,750 °F (704°C and 954°C).
8. The system of claim 1, wherein the NCGs are LCHV NCGs.
9. A process for reducing the accumulation of mid-kiln rings in an elongate rotary calcination kiln comprising: introducing NCGs into an elongate rotary calcination kiln, at an insertion location downstream of a burner end in a kiln chamber of an elongate rotary calcination kiln, wherein a temperature of the kiln chamber at the insertion location is in a range of 212 °F to 2,200 °F (100°C and about 1,204.44 °C).
10. The process of claim 9 further comprising not introducing the NCGs into the burner end of the elongate rotary calcination kiln.
11. The process of claim 9 further comprising introducing a compound at the insertion location with the NCGs, wherein the compound is selected from the group consisting of: air, ammonia, a sintering agent, urea, oxygen, re-circulated flue gas, and water vapor.
12. The process of claim 9, wherein the temperature at the insertion location is between about 1,300 °F and about 1,750 °F (704°C and 954°C).
13. The process of claim 9 further comprising measuring a first temperature at a first location upstream of the insertion location, measuring a second temperature at a second location downstream of the insertion location, comparing the first temperature to the second temperature to calculate a temperature difference, adding a cooling agent with the NCGs at the insertion location when the temperature difference is less than 100 °F (55.2°C).
14. The process of claim 13 further comprising ceasing to add the cooling agent when the temperature difference is 100 °F (55.2°C) or greater.
15. A process for reducing the accumulation of kiln rings in an elongate rotary calcination kiln comprising: feeding a calcine reactant into an elongate rotary calcination kiln at a feed end of the elongate rotary calcination kiln; oxidizing the calcine reactant in the elongate rotary calcination kiln with a burner disposed at a burner end of the elongate rotary calcination kiln, the burner end being distally disposed form the feed end; and introducing NCGs into the elongate rotary calcination kiln, through a plenum chamber annularly disposed around a tubular housing of the elongate rotary calcination kiln, wherein the plenum chamber fluidly communicates with a kiln chamber through an opening, and wherein a temperature of the kiln chamber is in a range of 1,300 °F to 1,750 °F (704°C to 954°C) at an insertion location.
16. The process of claim 15 further comprising adding air, water vapor, or cooled re- circulated flue gas to the plenum to control the temperature within the kiln chamber.
17. The process of claim 15 further comprising adding urea to the plenum to reduce the amount of nitrous oxides in exhaust gases.
18. The process of claim 8 further comprising adding water vapor to the plenum to regulate the temperature of the kiln chamber.
19. The process of claim 15 further comprising adding both urea and ammonia and the plenum to control the amount of nitrous oxides in the exhaust gasses.
20. The process of claim 15 further comprising measuring a first temperature at a first location upstream of the insertion location, measuring a second temperature at a second location downstream of the insertion location, comparing the first temperature to the second temperature to calculate a temperature difference, adding a cooling agent with the NCGs at the insertion location when the temperature difference is less than 100 °F (55.2°C).
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US62/564,087 | 2017-09-27 | ||
US16/133,365 | 2018-09-17 |
Publications (1)
Publication Number | Publication Date |
---|---|
NZ746788A true NZ746788A (en) |
Family
ID=
Similar Documents
Publication | Publication Date | Title |
---|---|---|
AU2018233011B2 (en) | Process And System For Reducing Ringing In Lime Kilns | |
CN106871131B (en) | For handling the device and method of industrial dangerous waste sodium sulfate salt slag and resource utilization | |
EA032282B1 (en) | Oxycombustion in a transport oxy-combustor | |
FI85424B (en) | FOERFARANDE FOER TORKNING AV FAST MATERIAL. | |
FI123110B (en) | Process and apparatus for treating the black liquor of a cellulose factory | |
CN104211271B (en) | A kind of two-period form mud gasification processing method and treating apparatus | |
BRPI0902045B1 (en) | Method to Treat Lime Mud | |
CN107721112B (en) | Municipal sludge drying pyrolysis gasification self-sustaining incineration system | |
CN116034094A (en) | Method for the physical and thermochemical treatment of biomass and treatment installation | |
NZ746788A (en) | Process And System For Reducing Ringing In Lime Kilns | |
RU2772158C2 (en) | Method and system for reducing ring formation in lime kilns | |
BR102018069618B1 (en) | ELONGATED ROTATORY CALCINATION FURNACE SYSTEM AND PROCESSES FOR REDUCING THE ACCUMULATION OF FURNACE RINGS IN AN ELONGATED ROTATORY CALCINATION FURNACE | |
CN101857266B (en) | Recovery method of alkali from pulping black liquor by direct causticization with rotary kiln gasifier | |
US11486090B2 (en) | Method and apparatus for burning odor gas | |
KR101875039B1 (en) | Fuel Additives and Fuel Additives Supply System for Coal Boilers Using Chemical Cleaning Wastewater | |
CN104235816B (en) | Fan mill and the coal of medium-speed pulverizer powder process and mud multifuel combustion green power generation system | |
KR20110008910A (en) | System and method of incinerating and processing wasted water | |
FI130505B (en) | A method for reducing combustion temperature and thermal radiation within a lime kiln | |
FI122837B (en) | Method for recovering chemicals from a pulp mill | |
CA1061059A (en) | Pulp mill recovery system | |
FI85993B (en) | Method for treatment of crude soap | |
SU1350450A2 (en) | Installation with recirculation of flue gases | |
Särkkä | Nitrogen oxide reduction in lime kiln gas burning | |
CN116592355A (en) | Multi-hearth combined grate type staged gasification combustion furnace | |
Richardson | Kraft lignin as a fuel for the rotary lime kiln |