PROCESS INSTRUMENTS ®

Cement and Lime Kilns PROCESS DESCRIPTION Cement, lime and gypsum manufacturing processes have in common the mixing of inorganic minerals calcined at high temperatures typically using rotary kilns (vertical kilns are also used).

CEMENT Regular Portland cements are the burning sinters and partially fuses The tremendously high temperature usual products for general concrete the ingredients into lumps known sustained by cement kilns and the

THERMOX construction. The raw materials, as clinkers. These clinkers are then long transit time are ideal for the limestone or chalk, together with cooled and pulverized into fine disposal of material such as tires or clay or shale are mixed and fed to a powder. Some gypsum is used to hazardous wastes. large rotary kiln at temperatures up control the speed of setting when to 2600°F (1427°C). The mix can be water is added. After the kiln, the taken through a number of preheater flue gas passes through various heat LIME and precalciner stages before being recovery stages, then to electrostatic Lime or quicklime are the common charged into the rotary kiln. precipitators for final clean up before names for calcium oxide (CaO), a being discharged to the stack. Kilns are normally fired with gray-white powder. Either directly APPLICATION NOTE pulverized coal or gas at one end. Some cement kilns are the or indirectly lime and limestone are Raw materials are fed to the kiln wet “slurry” type. Slurry of raw used in more industries than any at the back end furthest from the materials is fed directly into the other natural substance. It is used in burners. Travelling through the kiln, kiln. The temperature at the inlet is the manufacture of glass, cement, the ingredients are progressively considerably less than the dry feed brick, pulp/paper, steel, aluminum, heated. Here flue gas flows in the process. Also the kiln is much longer magnesium and poultry feed. It also opposite direction. The kiln can be to allow sufficient time for drying is used in processing cane and sugar divided into three zones - drying, before calcination. Figure 1 is a beet juices. Lime kilns are associated calcining and burning. Drying schematic of a typical cement plant. with every kraft pulp mill and often removes the water from the mix; used in steel mills. calcining drives off the carbon dioxide; Since lime is manufactured from quarried limestone, lime plants are located near these deposits. The crushed raw material is fed to a advantages of using thermox analyzers in rotary or vertical kiln where carbon lime, cement and other industries with rotary kilns dioxide is driven off to produce lime. The use of lime for any particular zx Measure O , Combustibles (CO + H ), and Methane 2 2 process depends on its composition zx Direct or indirect measurement and physical properties, which are zx Reliable sensor technology controlled by the selection of the limestone and manufacturing process zx Fast response details. The quality and color affect zx Ability to measure oxidizing or close to stoichiometric the suitability of use and price. zx Maximize fuel efficiency and product quality with reliable flue gas measurement zx Many options allow choice of analyzer style for optimum performance

www.thermox.com WHY FLUE GAS MONITORING?

®

QUARRYING RAW CRUSHING MATERIALS OPERATIONS

GRINDING

WET PROCESS DRY PROCESS

SLURRY DRY PRE-HEATER MIXING & MIXING & (OPTIONAL) BLENDING BLENDING

CLINKER CLINKER STORAGE COOLER PRE-CALCINER (OPTIONAL)

THERMOX GYPSUM

ROTARY KILN

PRODUCT FINISHING STACK STORAGE MILL PRECIPITATOR/ DRYING CALCINING BURNING or ZONE ZONE CLINKERING DUST REMOVAL ZONE

SHIPMENT SEPARATOR

Figure 1. Typical Cement Plant

Kiln operators aim to ensure consistent ❘❚ Safety Recent advances in sensor technology product quality along with good fuel Monitoring CO, combustibles and combined with alternative methods efficiency and increased production. methane can prevent build-up to the of mounting flue gas analyzers have Some reasons for flue gas monitoring levels that can cause an explosion in allowed much more dependable include: electrostatic precipitators, bag houses measurement of oxygen and carbon monoxide or combustibles in the flue or ID fans. CH4 is measured during the purge and light-off on kilns started up gas from rotary kilns. ❘❚ Efficiency with natural gas. In all combustion processes, monitoring As desirable as it is to measure for the flue gas for oxygen and combustibles above reasons, it is also very difficult (or CO) allows the process to be ❘❚ Emissions Reduction to measure the flue gas in cement operated more efficiently. At the high Significant reduction in emissions and lime kilns. This is due to the operating temperature of kilns, even of NOx and other pollutants can combination of high temperature, heavy a small reduction in excess air gives a be achieved by maintaining good particulate loading, and the tendency significant cost savings which makes combustion control. of the material to aggregate. It is monitoring particularly important. preferable to measure in the kiln ahead of the rotary seal so that air leakage ❘❚ ❘❚ Process Optimization and does not affect the reading. This often Product Quality necessitates a long probe, typically 9 ft. Maintaining the air/fuel ratio within a Control (2.7 m), which further compounds the specific range can be important for Reliable flue gas analysis provides difficulty. Figure 2 shows a schematic of product quality. For example, lime kilns information for effective control of kiln, the flue gas/burning section of the plant. use coal whenever possible due to the preheater, and precalciner conditions. high temperature and high cost of firing with natural gas. If the coal has a high sulfur content, it is necessary to operate ❘❚ Emissions Monitoring the kiln close to stoichiometric to avoid Continuous emissions monitoring systems (CEMS) are required for contamination of the lime with SO2. This is important for lime used in steel reporting emissions but are not normally manufacture or as a neutralizing agent used for process optimization.

for SO2 removal plants.

MEASURED GASES THERMOX

PREHEATER STORAGE TOWER SILO GAS CONDITIONING TOWER S T A C

K ®

COAL MILL

ELECTROSTATIC FLUE GAS FLOW PRECIPITATOR FEED FLOW OR FUEL BAG HOUSE

K IL N Figure 2. Flue Gas/Feed Schematic

Oxygen (O2) Carbon Monoxide (CO) and Methane (CH4)

Zirconium oxide-based oxygen Combustibles (CO+H2) Neither combustibles nor carbon analyzers can be used either directly Carbon monoxide analyzers are monoxide detectors are able to on the flue gas or connected to the infrared and can either be across- measure methane, the primary end of a sample conditioning system. the-stack or at the end of a sample constituent of natural gas. Before Paramagnetic or fuel cell-based oxygen conditioning system. The across-the- ignition of a natural gas burner, a analyzers must have a clean dry stack version can be used only after purge and light-off cycle aims to sample and therefore can be used only a sample clean up device such as an ensure that no gas is present, but after a sample conditioning system. electrostatic precipitator. Combustibles explosions still occur. An on-line methane measurement detects the detectors (CO and H2) are typically catalytic bead and are usually combined presence of natural gas before ignition with the oxygen measurement in the independently of the purge cycle. same analyzer. Most analyzers used on Once the burners are lit, methane no longer exists - only CO and H . sample conditioning systems are based 2 on paramagnetic, infrared, ultraviolet This measurement can be combined or electrochemical technology and with oxygen and combustibles in the require a perfectly clean, dry sample WDG-IVCM 3-in-1 analyzer. Due to the gas. If the sample conditioning system physical nature of gas-fired rotary kilns, fails to operate correctly, the cells of which can channel explosive energy, these analyzers become coated or methane detection can be of particular contaminated and are very expensive importance. to repair. METHODS OF FLUE GAS MONITORING

® There are many different ways of analyzer probe extends almost to the 2. Sample Conditioning Systems measuring the flue gas from rotary end of the deflector pipe, which is open A water-cooled probe or an automated/ kilns. All have been developed by in the direction opposite of the gas flow motorized probe ahead of the seal is customers through many years of trial shielded by the deflector. Others use a often connected to a sample system and error with their own process. The standard probe and filter with variable (refer to Figure 3, Probe 1). This customer knows the characteristics of success rates (see Figure 3, Probe 2). presents the cleaned, cooled flue the flue gas – temperature, stickiness gas to a bank of analyzers located in of the particulate, corrosivity, fluidity, an analyzer shelter. The analyzers and abrasiveness. He or she will Direct Measurement After the Seal are oxygen, carbon monoxide and generally know which kind of system A WDG-HPIIC (O and combustibles, 2 sometimes carbon dioxide used for is most likely to survive in the process. less than 1875°F/1024°C) or a WDG- process and combustion control. They There are as many different solutions Insitu (O only, less than 1250°F/677°C) 2 are easily damaged by sample system as there are plants. It is important can be used in the kiln hood or at any upsets and require frequent, if not daily, to work within the framework of the point in the flue gas flow path between calibration. customer’s experience. Most customers the kiln and the final stack. The A separate probe from the final prefer to measure at a point ahead of difficulty at the kiln hood is accessibility

THERMOX stack is used for continuous emission the rotating seal for precise control of for cleaning of the probe and service monitoring. The gases measured the kiln firing conditions without errors of the analyzer. The measurement include oxygen, CO, NOx, and SO . caused by the ingress of air from the in the hood can be influenced by air 2 seal. However, analysis can be made leakage past the rotating seal and The Thermox WDG-IVC or WDG- at any point between the kiln and the hence many customers prefer to have IVCM can replace the oxygen and CO final stack. Direct measurement works a sample taken from before the seal. analyzers used for process control for lower temperature, dry applications However it is often useful to measure on an existing sample system. The where ceramic is not required and the at other points in the process for good unistrut option allows the analyzer to particulates do not stick to the probe to combustion control and comparison. be mounted on a wall or panel in a build a large “beehive”. Making use of Both the WDG-Insitu and WDG-HPIIC convenient location. an existing sample system or a by- are diffusion-based analyzers and can pass is preferred for high temperature be used directly in high particulate applications, although some customers applications (see Figure 3, Probes 3 are measuring directly in the kiln and 4). with varying degrees of success and maintenance frequency. There is no single “best” way to monitor in Direct Measurement in the PreHeater kiln applications, but here are some As the temperature is normally cooler approaches. here (less than 1250°F/677°C), a WDG-HPIIC or a WDG-Insitu can be used directly mounted at a suitable 1. Direct Measurement point in the ductwork. Direct Measurement Before the Seal Direct measurement in the kiln ahead of the seal is the most difficult. 1 WATER WASH PROBE TO SAMPLE SYSTEM 2 WDG-INSITU Temperatures here are typically 1900° 3 WDG-HPIIC – 2200°F (1038° – 1204°C) on a dry 4 WDG-HPIIC FLOOR MOUNRT cement process and 800° – 1800°F (427° – 982°C) on a wet slurry cement process or a lime kiln. An insitu can be used if oxygen-only measurement is required and the temperature is under 1250°F/677°C. In many dry cement kilns, the temperature is high enough that only water-cooled probes can survive for extended operation. Some customers use a type of deflector pipe installed in the process with the Figure 3. Various Kiln Measurements analyzer mounted directly to this. The

METHODS OF FLUE GAS MONITORING THERMOX

FLOOR MOUNT WDG-HPIIC 3. By-Pass Systems MOUNTED TO FLANGE

In a by-pass system, the sample pipe is inserted into CLEANING the kiln behind the seal and routed out of the kiln to a PORT part of the ductwork at a slightly lower pressure. This causes the sample to flow through the by-pass and the 10" PIPE analyzer can be located at a suitable position. A fan AIR PURGE FLOOR may be required to assist the flow. A by-pass system still requires regular maintenance to keep it clean but SAMPLE the system can be designed with easy access ports. FAN (OPTIONAL) Figure 4 shows the analyzer mounted vertically on a ROTARY KILN larger diameter section of the by-pass. The version BRING TO LOWER shown in Figure 5 uses a Y-shaped pipe with the PRESSURE 4" SAMPLE LOCATION probe mounted horizontally in one of the arms of the Y. GAS PIPE

KILN GAS

Another approach brings the pipe to a large sample box ® upon which the analyzer (or multiple analyzers) can be mounted (Figure 6). Figure 4. By-Pass Vertical Probe

BLOWBACK AIR INLET

SAMPLE FROM KILN

FAN

Figure 5. By-Pass Horizontal Probe

INSPECTION/

CLEANING PORTS

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A p

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WDG- P

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HPIIC 3 E

KILN 8" '

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DUCT WORK

Figure 6. By-Pass Sample Box THERMOX APPLICATION NOTE APPLICATION

ELECTROSTATIC PRECIPITATOR VIBRATING PROTECTION PROCESS WALL For electrostatic precipitator protection, we recommend the WDG-IVCM, and WDG-HPIICM. Normally the combustibles high alarms are set to 0.8% at which point the precipitator or other devices can be shut down. PROBE Since a standard catalytic combustibles detector does NOT respond to methane, high levels of methane which may have leaked into the burner chamber at start up can lead to an explosion. A useful precaution in this case is to use an analyzer fitted with the additional methane detector.

FLEXIBLE MOUNT

® RELATED INDUSTRIES WITH KILNS ANALYZER ATTACHED TO FIRM SUPPORT In addition to cement and lime, rotary kilns are used for other applications. Some of the applications have considerable vibration which would damage the Figure 7. Flexible Mount analyzer. A flexible mount, shown in Figure 7, can be used to minimize the effect of vibration. An antivibration furnace is also recommended.

SUMMARY AMETEK/Thermox has a large installed base in rotary kiln measurement in the cement, lime, pulp and paper, steel, minerals, and waste disposal industries. The Thermox analyzers offer flexibility in design and options and can be adapted to practically any situation. We will be pleased to advise on your analytical application and invite you to contact your nearest AMETEK Process Instruments’ office for assistance.

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CHINA GERMANY © 2006, by AMETEK, Inc. Beijing / Tel: 86 10 8526 2111, Fax: 86 10 8526 2141 Tel: 49 21 59 91 36 0, Fax: 49 21 59 91 3680 All rights reserved. Printed in the U.S.A. Chengdu / Tel: 86 28 8675 8111, Fax: 86 28-8675 8141 MIDDLE EAST - Dubai appnote cement-lime (5/07) Shanghai / Tel: 86 21 6426 8111, Fax: 86 21 6426 7818 Tel: 971 4 881 2052, Fax: 971 4 881 2053 One of a family of innovative process analyzer solutions from AMETEK Process Instruments. SINGAPORE Specifications subject to change without notice. Tel: 65 6484 2388, Fax: 65 6481 6588