EP0244074B1 - Safety systems for coal pulverizing mills - Google Patents

Safety systems for coal pulverizing mills Download PDF

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Publication number
EP0244074B1
EP0244074B1 EP87302255A EP87302255A EP0244074B1 EP 0244074 B1 EP0244074 B1 EP 0244074B1 EP 87302255 A EP87302255 A EP 87302255A EP 87302255 A EP87302255 A EP 87302255A EP 0244074 B1 EP0244074 B1 EP 0244074B1
Authority
EP
European Patent Office
Prior art keywords
level
pulverizing mill
carbon monoxide
signal
mill
Prior art date
Legal status (The legal status 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 status listed.)
Expired - Lifetime
Application number
EP87302255A
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German (de)
English (en)
French (fr)
Other versions
EP0244074A3 (en
EP0244074A2 (en
Inventor
Scotty Young Jewett
John W. Robertson, Jr.
Gordon Davies Woolbert
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
INTERNATIONAL CONTROL AUTOMATION FINANCE SA
Original Assignee
International Control Automation Finance SA Luxembourg
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Publication date
Application filed by International Control Automation Finance SA Luxembourg filed Critical International Control Automation Finance SA Luxembourg
Publication of EP0244074A2 publication Critical patent/EP0244074A2/en
Publication of EP0244074A3 publication Critical patent/EP0244074A3/en
Application granted granted Critical
Publication of EP0244074B1 publication Critical patent/EP0244074B1/en
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
    • B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
    • B02C23/00—Auxiliary methods or auxiliary devices or accessories specially adapted for crushing or disintegrating not provided for in preceding groups or not specially adapted to apparatus covered by a single preceding group
    • B02C23/18—Adding fluid, other than for crushing or disintegrating by fluid energy
    • B02C23/24—Passing gas through crushing or disintegrating zone
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
    • B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
    • B02C23/00—Auxiliary methods or auxiliary devices or accessories specially adapted for crushing or disintegrating not provided for in preceding groups or not specially adapted to apparatus covered by a single preceding group
    • B02C23/04—Safety devices

Definitions

  • This invention relates to safety systems for coal pulverizing mills.
  • a number of commercial devices utilizing infrared absorption techniques are available for monitoring carbon monoxide levels in the pulverizing mill. This method is based upon the principle that when coal starts to oxidize, i.e. in the early stages of combustion, carbon monoxide is produced. Being able to detect this carbon monoxide at very low levels, e.g., 25 to 50 ppm, permits the mill operator to take precautionary measures to prevent a major fire or an explosion in the mill.
  • a small pocket of oxidizing coal can become a major fire through escalation or ignition. If escalation occurs, the oxidation process intensifies as the quality of coal involved and temperature increase. Larger quantities of carbon monoxide are produced as the process escalates until a runaway condition is reached which results in a fire. This small quantity of oxidizing coal also represents an ignition source which, combined with the other elements within the mill, can result in a major fire or explosion. In this case, the quantity of carbon monoxide does not need to escalate prior to the fire or explosion since the small pocket of oxidizing coal is only an ignition source.
  • European Patent Application EP-A 0 132 974 discloses a safety system for a coal pulverizer in which measurements of the net oxygen and carbon monoxide contents are taken, and alarm and/or automatic pulverizer inerting operations are initiated in response to the measurements.
  • a safety system for a coal pulverizing mill comprising:
  • the present invention can solve or at least alleviate the aforementioned problems associated with the prior art inasmuch as is is not dependent upon measuring temperature, gas flow velocity or only carbon monoxide for determining the existence of a potentially dangerous condition within the pulverizing mill.
  • a measurement of oxygen and/or an aggregate measurement of not only carbon monoxide but all combustible gases in the mill and/or a determination of the rate of change of such aggregate measurement is/are made and utilized for controlling the operation of the mill and/or warning the operator of a potentially dangerous mill condition.
  • a preferred embodiment of the invention described in detail hereinbelow incorporates a single point analyzer which is mounted directly to the pulverizing mill to provide continuous measurements of both the oxygen content and the carbon monoxide equivalent (CO e ) level of the pulverizing mill atmosphere.
  • the measurement of the carbon monoxide equivalent (CO e ) level includes not only the level of carbon monoxide in the pulverizing mill, but also the other combustible gases, such as hydrogen, methane, ethane, etc., in the mill.
  • the oxygen portion of the analyzer uses a sensor operating at a temperature at which any combustible volatile material will combine with the oxygen in the sample that is extracted from the pulverizing mill. The sensor will then respond to the free or uncombined oxygen remaining.
  • the resulting measurement is then compared with various predetermined setpoints and correlated with the carbon monoxide equivalent (CO e ) level, which is similarly compared with various predetermined setpoints, to determine if a potentially dangerous condition exists within the pulverizing mill.
  • CO e carbon monoxide equivalent
  • measurements of both the net oxygen (0 2 ) level and the carbon monoxide equivalent (COe) level in the pulverizing mill atmosphere are used to determine the onset of conditions within the mill which might lead to a fire or explosion in same.
  • the preferred embodiment thus provides an improved safety control system for detecting and controlling impending hazardous conditions in a coal pulverizing mill.
  • FIG. 1 is a schematic drawing of a safety control system 10 according to a preferred embodiment of the present invention.
  • the control system 10 can be integrated in a facility's control system designed to monitor the performance of and detect impending fire or explosions in industrial coal pulverizing mills by monitoring the net oxygen (0 2 ) level and the carbon monoxide equivalent (CO e ) level of the combustible components in the pulverizing mill atmosphere.
  • the measurement of the carbon monoxide equivalent (CO e ) level of the combustible components includes not only carbon monoxide but also other combustibles components such as hydrogen, methane, ethane and other higher hydrocarbon components.
  • the combined measurement of the CO e and net 0 2 levels in the pulverizing mill atmosphere is used to indicate the oxidation rate of the coal to prevent spontaneous combustion within the mill.
  • the measurement of the net 0 2 level when combined with other measurements, can provide the basis for overall mill performance calculations and the quality of the pulverized coal.
  • a CO e /0 2 sample probe 12 is usually placed in a coal pulverizing mill 14 outlet zone.
  • a sample gas is drawn through the probe 12 which is provided with a high temperature filter 16.
  • the filter 16 is required to maintain trouble-free operation of the control system 10 by minimizing the amount of particulate matter drawn into the analyzer.
  • a filter 16 which can be used for this application is of a type described in U.S. Patent No. US-A 4 286 472.
  • the air sample drawn from the coal pulverizer is then analyzed for percent by volume of oxygen (0 2 ) content and the carbon monoxide equivalent (CO e ) concentration of combustible components in ppm (parts per million) via a known oxygen and CO e gas analyzer 18 designed to operate in a harsh power plant environment and having autocalibration capabilities.
  • Electrical signals corresponding to the net oxygen (0 2 ) level i.e., the level of the free or uncombined oxygen within the sample remaining after the combustible volatile materials therein have combined with the oxygen in the sample, and the carbon monoxide equivalent (CO e ) level are transmitted respectively to a monitoring and control logic assembly 20 located in a central control room via lines 22 and 24.
  • the net 0 2 and CO e levels are displayed and/or recorded on a strip-chart recorder 26. If the net 0 2 level falls below a predetermined rise level, the system 10 actuates audible and visible alarms 28, 30, respectively, to alert the operator who, in turn, may manually take corrective action to inert the pulverizing mill 14 or permit the system 10 to continue until it initiates an automatic inert mode of operation to bring the pulverizing mill 14 operating parameters back under control.
  • the monitoring and control logic assembly 20 utilizes both the net oxygen (0 2 ) measurement provided by the analyzer 18 along line 22 as well as the carbon monoxide equivalent (CO e ) measurement provided along line 24 from the analyzer 18 to actuate the alarms 28, 30, respectively at a predetermined net oxygen (0 2 ) level and at a predetermined carbon monoxide equivalent (CO e ) rise level.
  • the net oxygen (0 2 ) level and/or the absolute carbon monoxide equivalent (COe) level exceed certain critical limits, automatic inerting of the pulverizing mill 14 is undertaken by controlling the opening of a valve 32 which permits some inertia media, such as carbon dioxide or steam, to flow along a line 34 into the pulverizing mill 14.
  • the net oxygen (0 2 ) measurement from line 22 is transmitted along a line 36 to a difference station 38 having a setpoint set at a predetermined net oxygen control point provided along a line 40.
  • the difference station 38 compares the actual net oxygen (0 2 ) measurement provided by the analyzer 18 with the setpoint net oxygen level and provides an error signal along a line 42 which is one input to an AND gate 44.
  • the other input to the AND gate 44 is provided by a constant negative signal from a predetermined source along a line 46.
  • the signal representative of the measured carbon monoxide equivalent (COe) level which is transmitted along line 24 may also provide an actuation of the alternative alarm 30.
  • the measured carbon monoxide equivalent (CO e ) level signal is transmitted to a derivative action controller 50 which is sensitive to any variations in the carbon monoxide equivalent (COe) level and provides an output signal along a line 52 indicative of the slope or rate of change of the carbon monoxide equivalent (CO e ) level in the pulverizing mill 14.
  • the output of the derivative action controller 50 is transmitted along line 52 to a difference station 54 having a predetermined setpoint provided along a line 56 representative of a rate of change of the carbon monoxide equivalent (CO e ) level which would indicate coal ignition in the pulverizing mill 14.
  • the output of the difference station 54 is transmitted along a line 58 to an AND gate 60 having a second input of a constant positive value provided along a line 62.
  • the rate of change of the carbon monoxide equivalent (CO e ) level normally stays below the setpoint applied to the difference station 54 resulting in a negative output signal from this station 54 along line 58.
  • the signal transmitted along line 58 becomes positive, causing the AND gate 60 to conduct resulting in the transmission of a control signal along a line 64 to the alarm 30 actuating same to indicate the existence of a potentially dangerous condition in the pulverizing mill 14.
  • CO e carbon monoxide equivalent
  • Automatic inerting of the pulverizing mill 14 is actuated by a difference station 66 which has a net oxygen level setpoint provided to it along a line 68.
  • the net oxygen level setpoint provided to the difference station 66 is significantly lower than the setpoint level provided to the difference station 38.
  • the net oxygen (0 2 ) level measured and transmitted to the difference station 66 will exceed the setpoint applied thereto and the error signal produced by the difference station 66 will be a positive signal which is transmitted along a line 70 to an AND gate 72.
  • the other input of the AND gate 72 is provided by a constant negative signal along a line 74.
  • the inputs to the AND gate 72 will be positive and negative, resulting in no control signal being transmitted from the AND gate 72 along a line 76.
  • the output of this station 66 becomes negative, providing two negative inputs to the AND gate 72 resulting in the transmission of a control signal along line 76 to a switching circuit 78.
  • the switching circuit 78 is a normally open circuit, preventing the signal from a controller 80 from reaching the control valve 32. When a control signal is present along line 76, the switching circuit 78 changes to a closed circuit condition, which results in the controller 80 being responsible for the operation of the valve 32.
  • One input to the controller 80 is the actual net oxygen (0 2 ) level in the pulverizing mill 14 and is provided by a line 82, which is connected to line 22.
  • the setpoint for the controller 80 is provided along a line 84 from some setpoint station and the level of this setpoint is typically between the setpoint levels for difference stations 66 and 38.
  • the switching circuit 78 is actuated by a control signal from the AND gate 72, indicating that the net oxygen (0 2 ) level within the pulverizing mill 14 has fallen below the setpoint level to the difference station 66, the controller 80 will open valve 32 causing an inerting atmosphere, such as carbon dioxide, to be delivered to the pulverizing mill 14 until a somewhat normal net oxygen level is reached close to the setpoint level for the controller 80.
  • the setpoint level for the controller 80 is kept somewhat lower than normal atmosphere to minimize the shock to the pulverizer 14 due to the inerting process.
  • the switching circuit 78 can then be reset to its normally open condition by a reset signal along a line 86 from either a manual source or an automatic source tied to some parameter indicative of the establishment of normal operating conditions within the pulverizing mill 14.
  • the actuation of the automatic inerting means is also alternatively done upon the sensing of a predetermined absolute carbon monoxide equivalent (Co e ) level in the pulverizing mill 14.
  • the carbon monoxide equivalent (COe) signal normally provided on line 24 is tapped by a line 88 to provide one input to a difference station 90.
  • the setpoint of the difference station 90 is provided along a line 92 from a setpoint station and the level of this setpoint is typically set at the maximum carbon monoxide equivalent (CO e ) level which can be tolerated in the pulverizing mill 14.
  • Oxygen, fuel and an ignition source must be present in the pulverizing mill in order for a fire or explosion to occur.
  • the grinding of the coal in the pulverizing mill releases hydrogen, methane, ethane and other combustible hydrocarbons. Carbon monoxide is present only in very low levels during the grinding process unless the oxidation process has commenced. Once the oxidation process has commenced and the coal temperature rises, all of the foregoing combustible gases will evolve and can be utilized as an indicator of a potentially dangerous condition.
  • Figure 3 shows the general relationship of the resulting carbon monoxide equivalent (CO e ) level in the pulverizing mill to the various combustible gaseous components which comprise same versus increasing coal temperature. As shown in Figure 3, measuring the aggregate of all these gaseous components produces a response that is significantly more pronounced than that based only upon carbon monoxide and eliminates the limitations resulting from relying on only one gas, viz., carbon monoxide.
  • FIG. 5 An example of a smoldering fire which did not ignite the pulverizing mill is shown in Figure 5.
  • the carbon monoxide equivalent (CO e ) level increased from 35 ppm to 225 ppm.
  • the carbon monoxide equivalent (COe) level remained at this high level and the net oxygen (0 2 ) level fell slightly from 17.75% to 16.75%.
  • the carbon monoxide equivalent (COe) and net oxygen (0 2 ) levels then returned to their normal levels.
  • Investigation of the pulverizing mill revealed a small quantity of coal smoldering in the mill for thirty minutes. The quantity of smoldering coal was not large enough to ignite the mill.
  • Figure 6 illustrates the general relationship of the carbon monoxide equivalent (CO e ) level, net oxygen (0 2 ) level, and pulverizer mill condition.
  • the normal operating band shows a general relationship between carbon monoxide equivalent (COe) level, net oxygen (0 2 ) level, and the type of coal used.
  • COe carbon monoxide equivalent
  • net oxygen (0 2 ) level As the percent volatile material in the coal increases, so does the expected carbon monoxide (CO e ) equivalent level. As the percent moisture increases, the net oxygen (0 2 ) level will decrease due to resulting higher moisture levels in the pulverizing mill gases.
  • Rises in the carbon monoxide equivalent (CO e ) level combined with a constant or dropping net oxygen (0 2 ) level indicates a smoldering condition with a potential for a pulverizer mill fire.

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  • Engineering & Computer Science (AREA)
  • Food Science & Technology (AREA)
  • Disintegrating Or Milling (AREA)
  • Crushing And Grinding (AREA)
EP87302255A 1986-04-29 1987-03-17 Safety systems for coal pulverizing mills Expired - Lifetime EP0244074B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US85770086A 1986-04-29 1986-04-29
US857700 1986-04-29

Publications (3)

Publication Number Publication Date
EP0244074A2 EP0244074A2 (en) 1987-11-04
EP0244074A3 EP0244074A3 (en) 1988-08-10
EP0244074B1 true EP0244074B1 (en) 1990-10-24

Family

ID=25326555

Family Applications (1)

Application Number Title Priority Date Filing Date
EP87302255A Expired - Lifetime EP0244074B1 (en) 1986-04-29 1987-03-17 Safety systems for coal pulverizing mills

Country Status (12)

Country Link
EP (1) EP0244074B1 (xx)
JP (1) JPS62258759A (xx)
KR (1) KR950001974B1 (xx)
AU (1) AU591260B2 (xx)
BR (1) BR8702407A (xx)
CA (1) CA1269150A (xx)
DE (1) DE3765686D1 (xx)
ES (1) ES2018824B3 (xx)
HK (1) HK42692A (xx)
IN (1) IN166429B (xx)
MX (1) MX168789B (xx)
SG (1) SG36192G (xx)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104152196A (zh) * 2014-05-30 2014-11-19 中国石油化工股份有限公司 煤岩油装置成套防爆方法
DE102011112741B4 (de) * 2011-09-07 2015-09-03 Werner Hofmann Inertgasgedeckte geschlossene Mahl-und Siebanlage
CN107797965A (zh) * 2017-10-23 2018-03-13 内蒙古岱海发电有限责任公司 一种磨煤机出口温度安全设定值的更新方法及系统

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FR2782023B1 (fr) * 1998-08-05 2000-09-08 Air Liquide Dispositif et procede de broyage de recipients fermes contenant une poudre
KR100460658B1 (ko) * 2000-06-29 2004-12-09 주식회사 포스코 미분탄제조장치의 산소농도분석 및 조절장치
KR100868440B1 (ko) * 2002-07-03 2008-11-11 주식회사 포스코 고로의 미분탄 제조설비의 배가스 제어 장치
JP4551101B2 (ja) * 2004-02-27 2010-09-22 三菱重工業株式会社 ミルイナート酸素濃度測定装置、ミルイナート酸素供給装置およびミルイナート酸素濃度測定方法
JP5385851B2 (ja) * 2010-05-17 2014-01-08 株式会社神戸製鋼所 粉砕機の発火防止方法及び発火防止装置
JP6057146B2 (ja) * 2012-04-25 2017-01-11 宇部興産機械株式会社 粉砕システム
KR101980178B1 (ko) * 2012-09-21 2019-05-20 한국전력공사 화재 감지 및 진화 장치를 구비하는 미분기
US9494319B2 (en) * 2013-03-15 2016-11-15 General Electric Technology Gmbh Pulverizer monitoring
CN106964474B (zh) * 2017-05-16 2018-04-20 安徽工业大学 一种磨煤机防爆检测系统
CN112536145B (zh) * 2020-11-20 2022-06-21 西安热工研究院有限公司 一种中速磨煤机运行安全在线监测与预警系统及方法
CN115301391B (zh) * 2022-08-04 2023-12-15 中国能源建设集团西北电力试验研究院有限公司 一种直吹式制粉系统智能控制停运方法

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US2799848A (en) * 1953-12-17 1957-07-16 Glantz Lester Murray Two-level control system
US3912015A (en) * 1974-06-17 1975-10-14 Armco Steel Corp System for the safe handling of pulverized coal
GB1485448A (en) * 1974-11-11 1977-09-14 Boc International Ltd Comminuting combustible material
US4031747A (en) * 1976-08-16 1977-06-28 Beckman Instruments, Inc. Misfire monitor for engine analysis having automatic rescaling
JPS5820247A (ja) * 1981-07-30 1983-02-05 バブコツク日立株式会社 ミル内の発火検知方法
KR900002655B1 (ko) * 1983-08-01 1990-04-21 더 뱁콕 앤드 윌콕스 컴퍼니 석탄미분쇄기의 안전제어시스템
JPS6094154A (ja) * 1983-10-28 1985-05-27 三菱重工業株式会社 防爆型粗大ごみ破砕機

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102011112741B4 (de) * 2011-09-07 2015-09-03 Werner Hofmann Inertgasgedeckte geschlossene Mahl-und Siebanlage
CN104152196A (zh) * 2014-05-30 2014-11-19 中国石油化工股份有限公司 煤岩油装置成套防爆方法
CN104152196B (zh) * 2014-05-30 2016-06-29 中国石油化工股份有限公司青岛安全工程研究院 煤岩油装置成套防爆方法
CN107797965A (zh) * 2017-10-23 2018-03-13 内蒙古岱海发电有限责任公司 一种磨煤机出口温度安全设定值的更新方法及系统

Also Published As

Publication number Publication date
MX168789B (es) 1993-06-08
EP0244074A3 (en) 1988-08-10
CA1269150A (en) 1990-05-15
KR870010430A (ko) 1987-11-30
DE3765686D1 (de) 1990-11-29
HK42692A (en) 1992-06-19
JPS62258759A (ja) 1987-11-11
KR950001974B1 (ko) 1995-03-08
ES2018824B3 (es) 1991-05-16
IN166429B (xx) 1990-05-05
AU7106387A (en) 1987-11-05
AU591260B2 (en) 1989-11-30
EP0244074A2 (en) 1987-11-04
SG36192G (en) 1992-05-22
BR8702407A (pt) 1988-02-17

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