343:, and were about 1.5 m in diameter and 15 m in length. Such a kiln made about 20 tonnes of clinker per day. The fuel, initially, was oil, which was readily available in Pennsylvania at the time. It was particularly easy to get a good flame with this fuel. Within the next 10 years, the technique of firing by blowing in pulverized coal was developed, allowing the use of the cheapest available fuel. By 1905, the largest kilns were 2.7 x 60 m in size, and made 190 tonnes per day. At that date, after only 15 years of development, rotary kilns accounted for half of world production. Since then, the capacity of kilns has increased steadily, and the largest kilns today produce around 10,000 tonnes per day. In contrast to static kilns, the material passes through quickly: it takes from 3 hours (in some old wet process kilns) to as little as 10 minutes (in short precalciner kilns). Rotary kilns run 24 hours a day, and are typically stopped only for a few days once or twice a year for essential maintenance. One of the main maintenance works on rotary kilns is tyre and roller surface machining and grinding works which can be done while the kiln works in full operation at speeds up to 3.5 rpm. This is an important discipline, because heating up and cooling down are long, wasteful, and damaging processes. Uninterrupted runs as long as 18 months have been achieved.
471:
encountered. Because these salts re-circulate back into the rawmix and re-enter the burning zone, a recirculation cycle establishes itself. A kiln with 0.1% chloride in the rawmix and clinker may have 5% chloride in the mid-kiln material. Condensation usually occurs in the preheater, and a sticky deposit of liquid salts glues dusty rawmix into a hard deposit, typically on surfaces against which the gas-flow is impacting. This can choke the preheater to the point that air-flow can no longer be maintained in the kiln. It then becomes necessary to manually break the build-up away. Modern installations often have automatic devices installed at vulnerable points to knock out build-up regularly. An alternative approach is to "bleed off" some of the kiln exhaust at the kiln inlet where the salts are still in the vapor phase, and remove and discard the solids in this. This is usually termed an "alkali bleed" and it breaks the recirculation cycle. It can also be of advantage for cement quality reasons, since it reduces the alkali content of the clinker. The alkali content is a critical property of cement. Indeed, cement with a too high alkali content can cause a harmful
378:
process. On the other hand, the wet process had a number of advantages. Wet grinding of hard minerals is usually much more efficient than dry grinding. When slurry is dried in the kiln, it forms a granular crumble that is ideal for subsequent heating in the kiln. In the dry process, it is very difficult to keep the fine powder rawmix in the kiln, because the fast-flowing combustion gases tend to blow it back out again. It became a practice to spray water into dry kilns in order to "damp down" the dry mix, and thus, for many years there was little difference in efficiency between the two processes, and the overwhelming majority of kilns used the wet process. By 1950, a typical large, wet process kiln, fitted with drying-zone heat exchangers, was 3.3 x 120 m in size, made 680 tonnes per day, and used about 0.25–0.30 tonnes of coal fuel for every tonne of clinker produced. Before the energy crisis of the 1970s put an end to new wet-process installations, kilns as large as 5.8 x 225 m in size were making 3000 tonnes per day.
414:
loaded onto the moving grate, and the hot combustion gases from the rear of the kiln are passed through the bed of pellets from beneath. This dries and partially calcines the rawmix very efficiently. The pellets then drop into the kiln. Very little powdery material is blown out of the kiln. Because the rawmix is damped in order to make pellets, this is referred to as a "semi-dry" process. The grate preheater is also applicable to the "semi-wet" process, in which the rawmix is made as a slurry, which is first de-watered with a high-pressure filter, and the resulting "filter-cake" is extruded into pellets, which are fed to the grate. In this case, the water content of the pellets is 17-20%. Grate preheaters were most popular in the 1950s and 60s, when a typical system would have a grate 28 m long and 4 m wide, and a rotary kiln of 3.9 x 60 m, making 1050 tonnes per day, using about 0.11-0.13 tonnes of coal fuel for every tonne of clinker produced. Systems up to 3000 tonnes per day were installed.
297:. The basic, egg-cup shaped lime kiln was provided with a conical or beehive shaped extension to increase draught and thus obtain the higher temperature needed to make cement clinker. For nearly half a century, this design, and minor modifications, remained the only method of manufacture. The kiln was restricted in size by the strength of the chunks of rawmix: if the charge in the kiln collapsed under its own weight, the kiln would be extinguished. For this reason, beehive kilns never made more than 30 tonnes of clinker per batch. A batch took one week to turn around: a day to fill the kiln, three days to burn off, two days to cool, and a day to unload. Thus, a kiln would produce about 1500 tonnes per year.
1546:) introduced into the burning process via the raw materials and fuels may evaporate completely or partially in the hot zones of the preheater and/or rotary kiln depending on their volatility, react with the constituents present in the gas phase, and condense on the kiln feed in the cooler sections of the kiln system. Depending on the volatility and the operating conditions, this may result in the formation of cycles that are either restricted to the kiln and the preheater or include the combined drying and grinding plant as well. Trace elements from the fuels initially enter the combustion gases, but are emitted to an extremely small extent only owing to the retention capacity of the kiln and the preheater.
467:, and if the raw materials are wet, hot gas from a less efficient preheater is desirable. For this reason, the most commonly encountered suspension preheaters have 4 cyclones. The hot feed that leaves the base of the preheater string is typically 20% calcined, so the kiln has less subsequent processing to do, and can therefore achieve a higher specific output. Typical large systems installed in the early 1970s had cyclones 6 m in diameter, a rotary kiln of 5 x 75 m, making 2500 tonnes per day, using about 0.11-0.12 tonnes of coal fuel for every tonne of clinker produced.
385:. Plants that burn waste fuels enjoy a negative fuel cost (they are paid by industries needing to dispose of materials that have energy content and can be safely disposed of in the cement kiln thanks to its high temperatures and longer retention times). As a result, the inefficiency of the wet process is an advantage—to the manufacturer. By locating waste burning operations at older wet process locations, higher fuel consumption actually equates to higher profits for the manufacturer, although it produces correspondingly greater emission of CO
611:
until recently. These consist of a set (typically 7–9) of tubes attached to the kiln tube. They have the advantage that they are sealed to the kiln, and require no separate drive. From about 1930, the grate cooler was developed. This consists of a perforated grate through which cold air is blown, enclosed in a rectangular chamber. A bed of clinker up to 0.5 m deep moves along the grate. These coolers have two main advantages: (1) they cool the clinker rapidly, which is desirable from a clinker quality point of view; it avoids that
1520:
vaporous, condense on the kiln feed or the kiln dust, at temperatures between 700 °C and 900 °C, subsequently re-enter the rotary kiln system and evaporate again. This cycle in the area between the rotary kiln and the preheater can result in coating formation. A bypass at the kiln inlet allows effective reduction of alkali chloride cycles and to diminish coating build-up problems. During the clinker burning process, gaseous inorganic chlorine compounds are either not emitted at all, or in very small quantities only.
332:, or pulverized solid fuel, is blown in through the "burner pipe", producing a large concentric flame in the lower part of the kiln tube. As material moves under the flame, it reaches its peak temperature, before dropping out of the kiln tube into the cooler. Air is drawn first through the cooler and then through the kiln for combustion of the fuel. In the cooler the air is heated by the cooling clinker, so that it may be 400 to 800 °C before it enters the kiln, thus causing intense and rapid combustion of the fuel.
285:. Typically, a peak temperature of 1400–1450 °C is required to complete the reaction. The partial melting causes the material to aggregate into lumps or nodules, typically of diameter 1–10 mm. This is called clinker. The hot clinker next falls into a cooler which recovers most of its heat, and cools the clinker to around 100 °C, at which temperature it can be conveniently conveyed to storage. The cement kiln system is designed to accomplish these processes.
750:
557:
makes 8,000–10,000 tonnes per day, using about 0.10-0.11 tonnes of coal fuel for every tonne of clinker produced. The kiln is dwarfed by the massive preheater tower and cooler in these installations. Such a kiln produces 3 million tonnes of clinker per year, and consumes 300,000 tonnes of coal. A diameter of 6 m appears to be the limit of size of rotary kilns, because the flexibility of the steel shell becomes unmanageable at or above this size, and the
861:
114:
603:
354:
511:
274:
362:
423:
519:
841:
case, the high gas temperatures (1000–1200 °C) cause almost instantaneous, complete and smokeless combustion of the tire. Alternatively, tires are chopped into 5–10 mm chips, in which form they can be injected into a precalciner combustion chamber. The steel and zinc in the tires become chemically incorporated into the clinker, partially replacing iron that must otherwise be fed as raw material.
101:. Over a billion tonnes of cement are made per year, and cement kilns are the heart of this production process: their capacity usually defines the capacity of the cement plant. As the main energy-consuming and greenhouse-gas–emitting stage of cement manufacture, improvement of kiln efficiency has been the central concern of cement manufacturing technology. Emissions from cement kilns are a major source of
692:
25:
455:
301:
the base to combust the fuel. The shaft kiln had a brief period of use before it was eclipsed by the rotary kiln, but it had a limited renaissance from 1970 onward in China and elsewhere, when it was used for small-scale, low-tech plants in rural areas away from transport routes. Several thousand such kilns were constructed in China. A typical shaft kiln produces 100-200 tonnes per day.
1320:(NO) dominates. This reaction is also called thermal NO formation. At the lower temperatures prevailing in a precalciner, however, thermal NO formation is negligible: here, the nitrogen bound in the fuel can result in the formation of what is known as fuel-related NO. Staged combustion is used to reduce NO: calciner fuel is added with insufficient combustion air. This causes CO to form.
1149:, kiln control is extremely challenging, because of multiple inter-related variables, non-linear responses, and variable process lags. Computer control systems were first tried in the early 1960s, initially with poor results due mainly to poor process measurements. Since 1990, complex high-level supervisory control systems have been standard on new installations. These operate using
317:
67:
1129:
be seen. Cameras, with or without infrared measurement capability, are mounted on the kiln hood to facilitate this. On many kilns, the same information can be inferred from the kiln motor power drawn, since sticky feed riding high on the kiln wall increases the eccentric turning load of the kiln. Further information can be obtained from the
733:) per tonne of clinker made. The gases carry a large amount of dust—typically 30 grams per cubic metre. Environmental regulations specific to different countries require that this be reduced to (typically) 0.1 gram per cubic metre, so dust capture needs to be at least 99.7% efficient. Methods of capture include
530:, and has subsequently become the equipment of choice for new large installations worldwide. The precalciner is a development of the suspension preheater. The philosophy is this: the amount of fuel that can be burned in the kiln is directly related to the size of the kiln. If part of the fuel necessary to burn the
777:) and hot flame is essential for this, high carbon fuels such as coal which produces a luminous flame are often preferred for kiln firing. Where it is cheap and readily available, natural gas is also sometimes used. However, because it produces a much less luminous flame, it tends to result in lower kiln output.
1042:
However, for efficient operation, steady conditions need to be maintained throughout the whole kiln system. The feed at each stage must be at a temperature such that it is "ready" for processing in the next stage. To ensure this, the temperature of both feed and gas must be optimized and maintained
872:
The objective of kiln operation is to make clinker with the required chemical and physical properties, at the maximum rate that the size of kiln will allow, while meeting environmental standards, at the lowest possible operating cost. The kiln is very sensitive to control strategies, and a poorly run
610:
Early systems used rotary coolers, which were rotating cylinders similar to the kiln, into which the hot clinker dropped. The combustion air was drawn up through the cooler as the clinker moved down, cascading through the air stream. In the 1920s, satellite coolers became common and remained in use
300:
Around 1885, experiments began on design of continuous kilns. One design was the shaft kiln, similar in design to a blast furnace. Rawmix in the form of lumps and fuel were continuously added at the top, and clinker was continually withdrawn at the bottom. Air was blown through under pressure from
1128:
and deduce the amount of liquid formation by experience. As more liquid forms, the clinker becomes stickier, and the bed of material climbs higher up the rising side of the kiln. It is usually also possible to assess the length of the zone of liquid formation, beyond which powdery "fresh" feed can
1030:
in which the reaction takes place. The amount of liquid, and hence the speed of the finishing reaction, is related to temperature. To meet the clinker quality objective, the most obvious control is that the clinker should reach a peak temperature such that the finishing reaction takes place to the
1022:
remain in the clinker. Regular measurement of the free CaO content is used as a means of tracking the clinker quality. As a parameter in kiln control, free CaO data is somewhat ineffective because, even with fast automated sampling and analysis, the data, when it arrives, may be 10 minutes "out of
703:
In indirect firing, the fuel is ground by an intermittently run mill, and the fine product is stored in a silo of sufficient size to supply the kiln though fuel mill stoppage periods. The fine fuel is metered out of the silo at a controlled rate and blown into the kiln. This method is now favoured
534:
is burned outside the kiln, the output of the system can be increased for a given kiln size. Users of suspension preheaters found that output could be increased by injecting extra fuel into the base of the preheater. The logical development was to install a specially designed combustion chamber at
470:
A penalty paid for the efficiency of suspension preheaters is their tendency to block up. Salts, such as the sulfate and chloride of sodium and potassium, tend to evaporate in the burning zone of the kiln. They are carried back in vapor form, and re-condense when a sufficiently low temperature is
462:
The number of cyclones stages used in practice varies from 1 to 6. Energy, in the form of fan-power, is required to draw the gases through the string of cyclones, and at a string of 6 cyclones, the cost of the added fan-power needed for an extra cyclone exceeds the efficiency advantage gained. It
1519:
are a minor additional constituents contained in the raw materials and fuels of the clinker burning process. They are released when the fuels are burnt or the kiln feed is heated, and primarily react with the alkalis from the kiln feed to form alkali chlorides. These compounds, which are initially
1443:
Rotary kilns of the cement industry and classic incineration plants mainly differ in terms of the combustion conditions prevailing during clinker burning. Kiln feed and rotary kiln exhaust gases are conveyed in counter-flow and mixed thoroughly. Thus, temperature distribution and residence time in
1311:
High process temperatures are required to convert the raw material mix to
Portland cement clinker. Kiln charge temperatures in the sintering zone of rotary kilns range at around 1450 °C. To reach these, flame temperatures of about 2000 °C are necessary. For reasons of clinker quality the
847:
For maximum kiln efficiency, high quality conventional fuels are the best choice. However, burning any fuels, especially hazardous waste materials, can result in toxic emissions. Thus, it is necessary for operators of cement kilns to closely monitor many process variables to ensure emissions are
720:
A large volume of gases has to be moved through the kiln system. Particularly in suspension preheater systems, a high degree of suction has to be developed at the exit of the system to drive this. Fans are also used to force air through the cooler bed, and to propel the fuel into the kiln. Fans
1422:
during the clinker burning process are caused by the small quantities of organic constituents input via the natural raw materials (remnants of organisms and plants incorporated in the rock in the course of geological history). These are converted during kiln feed preheating and become oxidized to
564:
A particular advantage of the air-separate precalciner is that a large proportion, or even 100%, of the alkali-laden kiln exhaust gas can be taken off as alkali bleed (see above). Because this accounts for only 40% of the system heat input, it can be done with lower heat wastage than in a simple
556:
to make clinker, and the rolling action of the rotary kiln remains the most efficient way of doing this. Large modern installations typically have two parallel strings of 4 or 5 cyclones, with one attached to the kiln and the other attached to the precalciner chamber. A rotary kiln of 6 x 100 m
413:
The grate preheater consists of a chamber containing a chain-like high-temperature steel moving grate, attached to the cold end of the rotary kiln. A dry-powder rawmix is turned into a hard pellets of 10–20 mm diameter in a nodulizing pan, with the addition of 10-15% water. The pellets are
1303:
contents in the exhaust gas of rotary kiln plants would in most cases considerably exceed the specifications of e.g. European legislation for waste burning plants (0.50 g/m for new plants and 0.80 g/m for existing plants). Reduction measures are aimed at smoothing and optimising plant operation.
840:
A notable example is the use of scrapped motor-vehicle tires, which are very difficult to dispose of by other means. Whole tires are commonly introduced in the kiln by rolling them into the upper end of a preheater kiln, or by dropping them through a slot midway along a long wet kiln. In either
2001:
The IPCC recommends using clinker data, rather than cement data, to estimate CO2 emissions because CO2 is emitted during clinker production and not during cement production. The Tier 1 method uses the IPCC default value for the fraction of lime in clinker, which is 64.6
699:
In direct firing, the fuel is fed at a controlled rate to the fuel mill, and the fine product is immediately blown into the kiln. The advantage of this system is that it is not necessary to store the hazardous ground fuel: it is used as soon as it is made. For this reason it was the system of
543:
The ultimate development is the "air-separate" precalciner, in which the hot combustion air for the calciner arrives in a duct directly from the cooler, bypassing the kiln. Typically, 60-75% of the fuel is burned in the precalciner. In these systems, the feed entering the rotary kiln is 100%
377:
The wet process suffered the obvious disadvantage that, when the slurry was introduced into the kiln, a large amount of extra fuel was used in evaporating the water. Furthermore, a larger kiln was needed for a given clinker output, because much of the kiln's length was committed to the drying
539:
is injected. This is referred to as an "air-through" precalciner, because the combustion air for both the kiln fuel and the calciner fuel all passes through the kiln. This kind of precalciner can burn up to 30% (typically 20%) of its fuel in the calciner. If more fuel were injected in the
1576:
in the section between the rotary kiln and the preheater, forming volatile compounds. Owing to the large surface area available, these compounds condense on the kiln feed particles at temperatures between 700 °C and 900 °C. In this way, the volatile elements accumulated in the
328:. The tube slopes slightly (1–4°) and slowly rotates on its axis at between 30 and 250 revolutions per hour. Rawmix is fed in at the upper end, and the rotation of the kiln causes it gradually to move downhill to the other end of the kiln. At the other end fuel, in the form of gas,
1444:
rotary kilns afford particularly favourable conditions for organic compounds, introduced either via fuels or derived from them, to be completely destroyed. For that reason, only very low concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (colloquially "
1589:
and its compounds are not precipitated in the kiln and the preheater. They condense on the exhaust gas route due to the cooling of the gas and are partially adsorbed by the raw material particles. This portion is precipitated in the kiln exhaust gas filter.
1415:. By contrast, the clinker burning process is a material conversion process that must always be operated with excess air for reasons of clinker quality. In concert with long residence times in the high-temperature range, this leads to complete fuel burn-up.
1532:
stable under the conditions of the burning process. Ultra-fine dust fractions that pass through the measuring gas filter may give the impression of low contents of gaseous fluorine compounds in rotary kiln systems of the cement industry.
1141:
in the clinker, and so also gives an indication of clinker temperature. Modern computer control systems usually make a "calculated" temperature, using contributions from all these information sources, and then set about controlling it.
450:
takes place: the gas is efficiently cooled, hence producing less waste of heat to the atmosphere, and the raw mix is efficiently heated. The heat transfer efficiency is further increased if a number of cyclones are connected in series.
1541:
The emission behaviour of the individual elements in the clinker burning process is determined by the input scenario, the behaviour in the plant and the precipitation efficiency of the dust collection device. The trace elements (e.g.,
876:
Formation of the desired clinker minerals involves heating the rawmix through the temperature stages mentioned above. The finishing transformation that takes place in the hottest part of the kiln, under the flame, is the reaction of
1583:(as the chloride) condenses in the upper zone of the cyclone preheater at temperatures between 450 °C and 500 °C. As a consequence, a cycle can be formed between preheater, raw material drying and exhaust gas purification.
1480:, which accounts for a share of more than 90% by mass. The rotary kiln systems of the cement industry destroy virtually completely the PAHs input via fuels. Emissions are generated from organic constituents in the raw material.
1116:
The assessment of the clinker peak temperature has always been problematic. Contact temperature measurement is impossible because of the chemically aggressive and abrasive nature of the hot clinker, and optical methods such as
671:
and, (2) because they do not rotate, hot air can be ducted out of them for use in fuel drying, or for use as precalciner combustion air. The latter advantage means that they have become the only type used in modern systems .
1464:
is comparable to that of dioxins and furans. PCB may be introduced into the process via alternative raw materials and fuels. The rotary kiln systems of the cement industry destroy these trace components virtually completely.
1162:
Emissions from cement works are determined both by continuous and discontinuous measuring methods, which are described in corresponding national guidelines and standards. Continuous measurement is primarily used for dust
1431:) are formed as well. In case of the clinker burning process, the content of CO and organic trace gases in the clean gas therefore may not be directly related to combustion conditions. The amount of released CO
369:
From the earliest times, two different methods of rawmix preparation were used: the mineral components were either dry-ground to form a flour-like powder, or were wet-ground with added water to produce a fine
1593:
Owing to trace element behaviour during the clinker burning process and the high precipitation efficiency of the dust collection devices, trace element emission concentrations are on a low overall level.
1153:
strategies, that maintain a "just sufficient" burning zone temperature, below which the kiln's operating condition will deteriorate catastrophically, thus requiring rapid-response, "knife-edge" control.
1252:
of up to 3,000 mg/m were measured leaving the stack of cement rotary kiln plants as recently as in the 1960s, legal limits are typically 30 mg/m today, and much lower levels are achievable.
1244:) must be ground to dust fineness during production. In this process, the steps of raw material processing, fuel preparation, clinker burning and cement grinding constitute major emission sources for
568:
The accompanying figures show the movement towards the use of the more efficient processes in North
America (for which data is readily available). But the average output per kiln in, for example,
438:
within the vessel. The gas leaves the vessel through a co-axial "vortex-finder". The solids are thrown to the outside edge of the vessel by centrifugal action, and leave through a valve in the
117:
A preheater tower, rawmix silo and exhaust stack. Bottom left: rawmill. Bottom right: rotary kiln with tertiary air duct above. The U-shaped duct leading from the kiln inlet is an "alkali bleed".
704:
for precalciner systems, because both the kiln and the precalciner can be fed with fuel from the same system. Special techniques are required to store the fine fuel safely, and coals with high
1039:, is extremely fluid. Cooling of the burning zone, and loss of unburned material into the cooler, is called "flushing", and in addition to causing lost production can cause massive damage.
1133:
analyzers. The formation of NO from nitrogen and oxygen takes place only at high temperatures, and so the NO level gives an indication of the combined feed and flame temperature. SO
544:
calcined. The kiln has only to raise the feed to sintering temperature. In theory the maximum efficiency would be achieved if all the fuel were burned in the preheater, but the
1091:
within the kiln which must be avoided at all costs since it causes destruction of the clinker mineral structure. For this reason, the exhaust gas is continually analyzed for
1909:, Nickolaos Chatziaras, Constantinos S. Psomopoulos, Nickolas J. Themelis, 2016, Management of Environmental Quality: An International Journal, Vol. 27 Iss 2 pp. 178 - 193,
1353:
is input into the clinker burning process via raw materials and fuels. Depending on their origin, the raw materials may contain sulfur bound as sulfide or sulfate. Higher
498:
is formed inside the reactive aggregates which develop characteristics internal fissures. This expansive chemical reaction occurring in the concrete matrix generate high
502:
in concrete and creates cracks that can ruine a concrete structure. However, hot gas is run to waste so the process is inefficient and increases kiln fuel consumption.
397:
In the 1930s, significantly, in
Germany, the first attempts were made to redesign the kiln system to minimize waste of fuel. This led to two significant developments:
565:
suspension preheater bleed. Because of this, air-separate precalciners are now always prescribed when only high-alkali raw materials are available at a cement plant.
700:
choice for older kilns. A disadvantage is that the fuel mill has to run all the time: if it breaks down, the kiln has to stop if no backup system is available.
773:, landfill off-gas and oil refinery flare gas. Because the clinker is brought to its peak temperature mainly by radiant heat transfer, and a bright (i.e. high
668:(as alite is responsible for the early strength development in cement setting and hardening, the highest possible content of the clinker in alite is desirable)
540:
calciner, the extra amount of air drawn through the kiln would cool the kiln flame excessively. The feed is 40-60% calcined before it enters the rotary kiln.
1360:
emissions by rotary kiln systems in the cement industry are often attributable to the sulfides contained in the raw material, which become oxidised to form SO
46:
1035:
material forms a dam that prevents the cooler upstream feed from flooding out of the kiln. The feed in the calcining zone, because it is a powder evolving
2019:
1183:), while the remaining parameters relevant pursuant to ambient pollution legislation are usually determined discontinuously by individual measurements.
381:
An interesting footnote on the wet process history is that some manufacturers have in fact made very old wet process facilities profitable through the
1902:
442:
of the cone. Cyclones were originally used to clean up the dust-laden gases leaving simple dry process kilns. If, instead, the entire feed of
1124:
are difficult because of the dust and fume-laden atmosphere in the burning zone. The traditional method of assessment was to view the bed of
849:
1240:
To manufacture 1 t of
Portland cement, about 1.5 to 1.7 t raw materials, 0.1 t coal and 1 t clinker (besides other cement constituents and
1056:
Exhaust fan speed or power: this controls gas flow, and the rate at which heat is drawn from the "hot end" of the system to the "cold end"
33:
1232:
emissions. Use of fuels with higher hydrogen content than coal and use of alternative fuels can reduce net greenhouse gas emissions.
995:) is thermodynamically unstable below 1250 °C, but can be preserved in a metastable state at room temperature by fast cooling (
1528:
Of the fluorine present in rotary kilns, 90 to 95% is bound in the clinker, and the remainder is bound with dust in the form of
1941:
1411:
and organically bound carbon are a yardstick for the burn-out rate of the fuels utilised in energy conversion plants, such as
2054:
2033:
1923:
1876:
1804:
1724:
1706:
Trend charts are based on USGS Annual
Reports (for detailed output) and Cembureau World Cement Reports (for process details).
721:
account for most of the electric power consumed in the system, typically amounting to 10–15 kW·h per tonne of clinker.
833:
the alkaline conditions in the kiln, afforded by the high-calcium rawmix, which can absorb acidic combustion products,
1655:
1445:
730:
1577:
kiln-preheater system are precipitated again in the cyclone preheater, remaining almost completely in the clinker.
1364:
at the temperatures between 370 °C and 420 °C prevailing in the kiln preheater. Most of the sulfides are
1473:
844:
A high level of monitoring of both the fuel and its combustion products is necessary to maintain safe operation.
1031:
required degree. A further reason to maintain constant liquid formation in the hot end of the kiln is that the
1372:
contained in the raw materials. Given the sulfide concentrations found e.g. in German raw material deposits, SO
1213:
emissions are both raw material-related and energy-related. Raw material-related emissions are produced during
1071:
The independent use of fan speed and fuel rate is constrained by the fact that there must always be sufficient
434:. A cyclone is a conical vessel into which a dust-bearing gas-stream is passed tangentially. This produces a
167:
In the second stage, the rawmix is fed into the kiln and gradually heated by contact with the hot gases from
1989:
2089:
1312:
burning process takes place under oxidising conditions, under which the partial oxidation of the molecular
848:
continuously minimized. In the U.S., cement kilns are regulated as a major source of air pollution by the
257:
1300 to 1450 °C – partial (20–30%) melting takes place, and belite reacts with calcium oxide to form
1399:
sulfates, which are bound in the clinker, provided that oxidizing conditions are maintained in the kiln.
830:
the temperatures in the kiln, which are much higher than in other combustion systems (e.g. incinerators),
1476:(according to EPA 610) in the exhaust gas of rotary kilns usually appear at a distribution dominated by
1376:
emission concentrations can total up to 1.2 g/m depending on the site location. In some cases, injected
1272:). The amount formed is directly related to the main flame temperature (typically 1850–2000 °C).
734:
472:
1899:
1611:
785:
In addition to these primary fuels, various combustible waste materials have been fed to kilns. These
1419:
1186:
The following descriptions of emissions refer to modern kiln plants based on dry process technology.
182:
400 to 600 °C – clay-like minerals are decomposed into their constituent oxides; principally SiO
1856:
1461:
536:
102:
1508:
is formed during the thermal decomposition of organic raw material constituents in the preheater.
389:. Manufacturers who think such emissions should be reduced are abandoning the use of wet process.
949:
38:
480:
293:
Portland cement clinker was first made (in 1825) in a modified form of the traditional static
738:
2044:
1549:
Under the conditions prevailing in the clinker burning process, non-volatile elements (e.g.
1428:
729:
The exhaust gases from a modern kiln typically amount to 2 tonnes (or 1500 cubic metres at
1053:
Fuel injection rate: this controls the rate at which the "hot end" of the system is heated
8:
813:
431:
1264:
The clinker burning process is a high-temperature process resulting in the formation of
1693:
1050:
Rotary kiln speed: this controls the rate at which the feed moves through the kiln tube
1026:
Conversion of belite to alite requires partial melting, the resulting liquid being the
803:
1945:
2079:
2050:
2029:
1872:
1800:
1720:
1651:
1619:
1586:
1377:
1317:
1273:
865:
340:
221:
90:
1927:
826:
Cement kilns are an attractive way of disposing of hazardous materials, because of:
175:. Successive chemical reactions take place as the temperature of the rawmix rises:
1864:
1529:
1277:
1195:
1125:
786:
553:
152:
98:
2074:
2023:
1906:
1408:
1146:
1138:
1099:
1084:
820:
495:
382:
282:
225:
195:
94:
82:
70:
Hot end of medium-sized modern cement kiln, showing tyres, rollers and drive gear
1868:
2084:
2002:
percent. This results in an emission factor of 0.507 tons of CO2/ton of clinker
1354:
1265:
1203:
1180:
1172:
1107:
1080:
1036:
793:
762:
499:
439:
211:
78:
1910:
2068:
1623:
1412:
1150:
1019:
798:
646:
447:
247:
1987:
1391:
during combustion in the rotary kiln. In the preheater and the kiln, this SO
1543:
1497:
1164:
1103:
808:
374:
with the consistency of paint, and with a typical water content of 40–45%.
336:
1504:
are present in the exhaust gas of rotary kilns in a characteristic ratio.
1043:
at every point. The external controls available to achieve this are few:
1023:
date", and more immediate data must be used for minute-to-minute control.
664: (an exothermic reaction favored by the heat release),
353:
1477:
1285:
1245:
1130:
968:
770:
510:
491:
324:
The rotary kiln consists of a tube made from steel plate, and lined with
305:
160:
749:
580:
Essential equipment in addition to the kiln tube and the preheater are:
361:
105:, accounting for around 2.5% of non-natural carbon emissions worldwide.
774:
705:
558:
518:
168:
463:
is normal to use the warm exhaust gas to dry the raw materials in the
1369:
1214:
1121:
1032:
996:
836:
the ability of the clinker to absorb heavy metals into its structure.
766:
545:
484:
329:
325:
294:
145:
126:
1067:
Independent fan controls where there are multiple preheater strings.
860:
602:
246:
900 to 1050 °C – the remaining calcium carbonate decomposes to
113:
1580:
1573:
1554:
1516:
1313:
1118:
569:
476:
1060:
In the case of precalciner kilns, further controls are available:
273:
1569:
1550:
1493:
1489:
1241:
1027:
549:
464:
422:
138:
1483:
24:
1558:
1501:
1396:
1365:
1350:
1092:
1087:
is formed, this represents a waste of fuel, and also indicates
1076:
1072:
1000:
878:
691:
629:
531:
487:
443:
435:
371:
232:
156:
86:
1284:) for about 5% of this compound present in the exhaust gas of
606:
A pair of kilns with satellite coolers in Ashaka, Nigeria Sysy
316:
308:, which today accounts for more than 95% of world production.
1942:"Regulatory Actions | Portland Cement Manufacturing | US EPA"
1511:
1452:") can be found in the exhaust gas from cement rotary kilns.
1449:
1387:
The sulfur input with the fuels is completely converted to SO
1088:
901:
868:
with automatic sample feed for free calcium oxide measurement
612:
527:
454:
258:
134:
1924:"Basic Information | Portland Cement Manufacturing | US EPA"
1523:
1338:
Hot tertiary air is then added to oxidize the remaining CO.
852:
and must meet stringent air pollution control requirements.
628:), thermodynamically unstable below 1250 °C, revert to
1996:
1565:
1505:
1308:(SNCR) are applied to cope with the emission limit values.
1305:
1249:
758:
172:
130:
121:
A typical process of manufacture consists of three stages:
1427:. In this process, small portions of organic trace gases (
2042:
1468:
1018:
If the reaction is incomplete, excessive amounts of free
430:
The key component of the gas-suspension preheater is the
66:
16:
High temperature rotating oven used for producing clinker
1857:"Coal utilisation in the cement and concrete industries"
1402:
446:
is forced to pass through the cyclone, a very efficient
1900:
Use of waste derived fuels in cement industry: a review
1075:
available to burn the fuel, and in particular, to burn
335:
The earliest successful rotary kilns were developed in
1681:
Calcareous
Cements: their Nature, Manufacture and Uses
346:
873:
kiln can easily double cement plant operating costs.
757:
Fuels that have been used for primary firing include
753:
Used tires being fed mid-kiln to a pair of long kilns
1322:
The CO then reduces the NO into molecular nitrogen:
1316:
in the combustion air resulting in the formation of
108:
1572:preferentially react with the excess chlorides and
708:
are normally milled in an inert atmosphere (e.g. CO
1988:Michael J. Gibbs, Peter Soyka and David Conneely.
1536:
1455:
522:Mean Daily Output (tonnes) of North American Kilns
304:From 1885, trials began on the development of the
148:temperature (up to 1450 °C) in a cement kiln;
1854:
2066:
1795:Section 4.1; R H Perry, C H Chilton, D W Green,
1064:Independent control of fuel to kiln and calciner
1209:accounts for the main share of these gases. CO
514:% of North American Capacity using Precalciners
1438:
1299:Without reduction measures, process-related NO
680:Fuel systems are divided into two categories:
526:In the 1970s the precalciner was pioneered in
357:% of North American Capacity using Wet Process
1895:
1893:
1861:The Coal Handbook: Towards Cleaner Production
1668:A Hundred Years of Portland Cement, 1824-1924
1484:Benzene, toluene, ethylbenzene, xylene (BTEX)
365:Mean Fuel Energy used in North American Kilns
269:) (also known as C3S in the Cement Industry).
243:) (also known as C2S in the Cement Industry).
179:70 to 110 °C – Free water is evaporated.
1292:in the atmosphere, emissions are given as NO
1288:plants. As most of the NO is converted to NO
417:
1911:https://dx.doi.org/10.1108/MEQ-01-2015-0012
561:lining tends to fail when the kiln flexes.
281:Alite is the characteristic constituent of
1890:
1512:Gaseous inorganic chlorine compounds (HCl)
1670:, Concrete Publications Ltd, London, 1924
1524:Gaseous inorganic fluorine compounds (HF)
999:): on slow cooling it tends to revert to
971:reaction favored by a higher temperature)
1435:is about half a ton per ton of clinker.
1255:
1228:) and account for about half of total CO
1157:
859:
748:
690:
601:
517:
509:
453:
426:Cutaway view of cyclone showing air path
421:
360:
352:
315:
272:
112:
65:
49:of all important aspects of the article.
1561:) are completely bound in the clinker.
1341:
1047:Feed rate: this defines the kiln output
458:4-Stage preheater, showing path of feed
206:) decomposes to calcium carbonate (CaCO
97:-bearing minerals to form a mixture of
2067:
2046:Lea's Chemistry of Cement and Concrete
2018:
1990:"Co2 emissions from cement production"
1648:Lea's Chemistry of Cement and Concrete
1469:Polycyclic aromatic hydrocarbons (PAH)
1137:is formed by thermal decomposition of
575:
535:the base of the preheater, into which
45:Please consider expanding the lead to
1403:Carbon monoxide (CO) and total carbon
2043:Peter Hewlett; Martin Liska (2019).
1855:Schumacher, G.; Juniper, L. (2013),
1797:Perry's Chemical Engineers' Handbook
1306:Selective Non-Catalytic NO Reduction
780:
18:
1304:Technically, staged combustion and
408:
347:The wet process and the dry process
13:
2011:
1694:"Cement Kilns: Early rotary kilns"
1407:The exhaust gas concentrations of
339:around 1890, based on a design by
311:
14:
2101:
1644:The History of Calcareous Cements
1276:(NO) accounts for about 95%, and
1189:
109:The manufacture of cement clinker
1818:op cit Sections 12.1, 12.2, 18.5
572:is twice that in North America.
288:
23:
1981:
1969:
1952:
1934:
1916:
1848:
1835:
1822:
1810:
1785:
1768:
1679:G R Redgrave & C Spackman,
1537:Trace elements and heavy metals
1456:Polychlorinated biphenyls (PCB)
855:
724:
593:Exhaust gas cleaning equipment.
505:
320:General layout of a rotary kiln
37:may be too short to adequately
1863:, Elsevier, pp. 387–426,
1751:
1734:
1709:
1700:
1686:
1673:
1660:
1636:
1604:
47:provide an accessible overview
1:
1799:, 7th Ed, McGraw-Hill, 1997,
1597:
1296:per cubic metre exhaust gas.
900:) with calcium oxide to form
744:
675:
404:the gas-suspension preheater.
392:
137:to make a fine "rawmix" (see
85:and other types of hydraulic
7:
1869:10.1533/9781782421177.3.387
1439:Dioxins and furans (PCDD/F)
737:and bag-filters. See also
735:electrostatic precipitators
548:operation involves partial
10:
2106:
1460:The emission behaviour of
597:
2049:. Butterworth-Heinemann.
418:Gas-suspension preheaters
1650:, 4th Ed, Arnold, 1998,
1420:organically bound carbon
1418:The emissions of CO and
948:Also abbreviated in the
794:Used motor-vehicle tires
103:greenhouse gas emissions
81:stage of manufacture of
1727:, Chapter 2 , Hewlett
1612:"Cracks in the surface"
1235:
950:cement chemist notation
715:
277:Typical clinker nodules
151:grinding the resulting
1717:The Rotary Cement Kiln
967: (
869:
754:
696:
607:
523:
515:
473:alkali–silica reaction
459:
427:
366:
358:
321:
278:
144:heating the rawmix to
125:grinding a mixture of
118:
71:
1646:in P C Hewlett (Ed),
1250:particulate emissions
1158:Cement kiln emissions
976:Tricalcium silicate (
863:
752:
739:cement kiln emissions
694:
649:(C) on slow cooling:
605:
521:
513:
457:
425:
364:
356:
319:
276:
220:650 to 900 °C –
116:
69:
1962:Chapter 14, Hewlett
1778:Chapter 18; Hewlett
1429:total organic carbon
483:containing reactive
2090:Industrial furnaces
2020:Taylor, Harry F. W.
1719:, CHS Press, 1998,
1380:is used to lower SO
1256:Nitrogen oxides (NO
1089:reducing conditions
819:Chemical and other
814:Refuse-derived fuel
576:Ancillary equipment
401:the grate preheater
2028:. Thomas Telford.
1905:2016-10-24 at the
1342:Sulfur dioxide (SO
1326:2 CO + 2 NO → 2 CO
1248:components. While
1198:burning process CO
1145:As an exercise in
870:
804:Agricultural waste
755:
697:
608:
524:
516:
460:
428:
383:use of waste fuels
367:
359:
322:
279:
119:
72:
2056:978-0-08-100795-2
2035:978-0-7277-2592-9
1878:978-1-78242-116-0
1805:978-0-07-049841-9
1725:978-0-8206-0367-4
1564:Elements such as
1378:calcium hydroxide
1318:nitrogen monoxide
1274:Nitrogen monoxide
866:X-ray diffraction
787:alternative fuels
781:Alternative fuels
341:Frederick Ransome
222:calcium carbonate
99:calcium silicates
91:calcium carbonate
77:are used for the
64:
63:
2097:
2060:
2039:
2025:Cement Chemistry
2005:
2004:
1994:
1985:
1979:
1973:
1967:
1956:
1950:
1949:
1944:. Archived from
1938:
1932:
1931:
1926:. Archived from
1920:
1914:
1897:
1888:
1887:
1886:
1885:
1852:
1846:
1839:
1833:
1826:
1820:
1814:
1808:
1789:
1783:
1772:
1766:
1755:
1749:
1738:
1732:
1713:
1707:
1704:
1698:
1697:
1690:
1684:
1677:
1671:
1664:
1658:
1640:
1634:
1633:
1631:
1630:
1608:
1530:calcium fluoride
1278:nitrogen dioxide
1227:
1013:
994:
983:
966:
944:
922:
899:
663:
644:
642:
641:
627:
625:
624:
496:sodium silicagel
409:Grate preheaters
59:
56:
50:
27:
19:
2105:
2104:
2100:
2099:
2098:
2096:
2095:
2094:
2065:
2064:
2063:
2057:
2036:
2014:
2012:Further reading
2009:
2008:
1999:. p. 177.
1992:
1986:
1982:
1974:
1970:
1957:
1953:
1940:
1939:
1935:
1922:
1921:
1917:
1913:, 08 March 2016
1907:Wayback Machine
1898:
1891:
1883:
1881:
1879:
1853:
1849:
1840:
1836:
1827:
1823:
1815:
1811:
1790:
1786:
1773:
1769:
1756:
1752:
1739:
1735:
1714:
1710:
1705:
1701:
1692:
1691:
1687:
1678:
1674:
1665:
1661:
1641:
1637:
1628:
1626:
1610:
1609:
1605:
1600:
1539:
1526:
1514:
1486:
1471:
1458:
1441:
1434:
1426:
1405:
1395:reacts to form
1394:
1390:
1383:
1375:
1363:
1358:
1348:
1345:
1333:
1329:
1321:
1302:
1295:
1291:
1283:
1271:
1266:nitrogen oxides
1262:
1259:
1238:
1231:
1226:
1222:
1218:
1217:decarbonation (
1212:
1207:
1201:
1192:
1178:
1173:nitrogen oxides
1170:
1160:
1147:process control
1139:calcium sulfate
1136:
1111:
1096:
1085:carbon monoxide
1012:
1008:
1004:
993:
989:
985:
981:
977:
964:
960:
956:
943:
939:
935:
931:
927:
921:
917:
913:
909:
905:
898:
894:
890:
886:
882:
858:
821:hazardous waste
783:
747:
727:
718:
711:
687:Indirect firing
678:
661:
657:
653:
640:
637:
636:
635:
633:
623:
620:
619:
618:
616:
600:
578:
537:pulverized coal
508:
420:
411:
395:
388:
349:
314:
312:The rotary kiln
291:
283:Portland cement
268:
264:
253:
242:
238:
229:
215:
209:
205:
201:
193:
189:
185:
111:
60:
54:
51:
44:
32:This article's
28:
17:
12:
11:
5:
2103:
2093:
2092:
2087:
2082:
2077:
2062:
2061:
2055:
2040:
2034:
2015:
2013:
2010:
2007:
2006:
1980:
1968:
1951:
1948:on 2013-01-01.
1933:
1930:on 2015-07-17.
1915:
1889:
1877:
1847:
1834:
1821:
1809:
1784:
1767:
1750:
1733:
1708:
1699:
1685:
1683:, London, 1924
1672:
1659:
1635:
1618:. 2016-08-25.
1602:
1601:
1599:
1596:
1538:
1535:
1525:
1522:
1513:
1510:
1485:
1482:
1470:
1467:
1457:
1454:
1440:
1437:
1432:
1424:
1423:form CO and CO
1413:power stations
1404:
1401:
1392:
1388:
1381:
1373:
1361:
1356:
1347:
1343:
1340:
1336:
1335:
1331:
1327:
1300:
1293:
1289:
1281:
1269:
1261:
1257:
1254:
1242:sulfate agents
1237:
1234:
1229:
1224:
1220:
1210:
1205:
1199:
1191:
1190:Carbon dioxide
1188:
1181:sulfur dioxide
1176:
1168:
1159:
1156:
1134:
1109:
1094:
1081:carbon dioxide
1069:
1068:
1065:
1058:
1057:
1054:
1051:
1048:
1037:carbon dioxide
1016:
1015:
1010:
1006:
991:
987:
979:
973:
972:
962:
958:
946:
945:
941:
937:
933:
929:
919:
915:
911:
907:
896:
892:
888:
884:
857:
854:
838:
837:
834:
831:
824:
823:
817:
811:
806:
801:
796:
789:(AF) include:
782:
779:
767:heavy fuel oil
763:petroleum coke
746:
743:
726:
723:
717:
714:
709:
689:
688:
685:
677:
674:
666:
665:
659:
655:
638:
621:
599:
596:
595:
594:
591:
588:
585:
577:
574:
507:
504:
500:tensile stress
419:
416:
410:
407:
406:
405:
402:
394:
391:
386:
348:
345:
313:
310:
290:
287:
271:
270:
266:
262:
255:
251:
244:
240:
236:
227:
218:
213:
207:
203:
199:
191:
187:
183:
180:
165:
164:
149:
142:
110:
107:
79:pyroprocessing
62:
61:
41:the key points
31:
29:
22:
15:
9:
6:
4:
3:
2:
2102:
2091:
2088:
2086:
2083:
2081:
2078:
2076:
2073:
2072:
2070:
2058:
2052:
2048:
2047:
2041:
2037:
2031:
2027:
2026:
2021:
2017:
2016:
2003:
1998:
1991:
1984:
1978:
1972:
1965:
1961:
1955:
1947:
1943:
1937:
1929:
1925:
1919:
1912:
1908:
1904:
1901:
1896:
1894:
1880:
1874:
1870:
1866:
1862:
1858:
1851:
1844:
1838:
1831:
1825:
1819:
1813:
1806:
1802:
1798:
1794:
1788:
1781:
1777:
1771:
1764:
1760:
1754:
1748:, pp 73,74,76
1747:
1743:
1737:
1730:
1726:
1722:
1718:
1712:
1703:
1695:
1689:
1682:
1676:
1669:
1663:
1657:
1656:0-340-56589-6
1653:
1649:
1645:
1642:R G Blezard,
1639:
1625:
1621:
1617:
1616:The Economist
1613:
1607:
1603:
1595:
1591:
1588:
1584:
1582:
1578:
1575:
1571:
1567:
1562:
1560:
1556:
1552:
1547:
1545:
1534:
1531:
1521:
1518:
1509:
1507:
1503:
1499:
1495:
1491:
1481:
1479:
1475:
1466:
1463:
1453:
1451:
1447:
1436:
1430:
1421:
1416:
1414:
1410:
1400:
1398:
1385:
1379:
1371:
1367:
1359:
1352:
1339:
1325:
1324:
1323:
1319:
1315:
1309:
1307:
1297:
1287:
1279:
1275:
1267:
1253:
1251:
1247:
1243:
1233:
1216:
1208:
1197:
1187:
1184:
1182:
1174:
1166:
1155:
1152:
1151:expert system
1148:
1143:
1140:
1132:
1127:
1123:
1120:
1114:
1112:
1105:
1101:
1097:
1090:
1086:
1082:
1078:
1074:
1066:
1063:
1062:
1061:
1055:
1052:
1049:
1046:
1045:
1044:
1040:
1038:
1034:
1029:
1024:
1021:
1020:calcium oxide
1002:
998:
975:
974:
970:
955:
954:
953:
951:
926:
925:
924:
903:
880:
874:
867:
862:
853:
851:
845:
842:
835:
832:
829:
828:
827:
822:
818:
815:
812:
810:
807:
805:
802:
800:
799:Sewage sludge
797:
795:
792:
791:
790:
788:
778:
776:
772:
768:
764:
760:
751:
742:
740:
736:
732:
722:
713:
707:
701:
693:
686:
684:Direct firing
683:
682:
681:
673:
669:
652:
651:
650:
648:
631:
614:
604:
592:
589:
586:
583:
582:
581:
573:
571:
566:
562:
560:
555:
551:
547:
541:
538:
533:
529:
520:
512:
503:
501:
497:
494:and swelling
493:
489:
486:
482:
478:
474:
468:
466:
456:
452:
449:
448:heat exchange
445:
441:
437:
433:
424:
415:
403:
400:
399:
398:
390:
384:
379:
375:
373:
363:
355:
351:
344:
342:
338:
333:
331:
327:
318:
309:
307:
302:
298:
296:
289:Early history
286:
284:
275:
260:
256:
249:
248:calcium oxide
245:
234:
230:
223:
219:
216:
197:
181:
178:
177:
176:
174:
170:
162:
158:
154:
150:
147:
143:
140:
136:
132:
128:
124:
123:
122:
115:
106:
104:
100:
96:
92:
88:
84:
80:
76:
68:
58:
48:
42:
40:
35:
30:
26:
21:
20:
2045:
2024:
2000:
1983:
1976:
1971:
1963:
1959:
1954:
1946:the original
1936:
1928:the original
1918:
1882:, retrieved
1860:
1850:
1842:
1837:
1829:
1824:
1817:
1812:
1796:
1792:
1787:
1779:
1775:
1770:
1762:
1758:
1753:
1745:
1741:
1736:
1728:
1716:
1711:
1702:
1688:
1680:
1675:
1667:
1662:
1647:
1643:
1638:
1627:. Retrieved
1615:
1606:
1592:
1585:
1579:
1563:
1548:
1544:heavy metals
1540:
1527:
1515:
1498:ethylbenzene
1487:
1472:
1459:
1442:
1417:
1406:
1386:
1349:
1337:
1310:
1298:
1263:
1239:
1202:is emitted.
1193:
1185:
1165:particulates
1161:
1144:
1115:
1070:
1059:
1041:
1025:
1017:
947:
910:S = 3CaO·SiO
887:S = 2CaO·SiO
875:
871:
856:Kiln control
846:
843:
839:
825:
809:Landfill gas
784:
756:
728:
725:Gas cleaning
719:
702:
698:
695:Cement plant
679:
670:
667:
662:S + C + heat
609:
579:
567:
563:
554:nodulization
542:
525:
506:Precalciners
469:
461:
429:
412:
396:
380:
376:
368:
350:
337:Pennsylvania
334:
323:
303:
299:
292:
280:
250:(CaO) and CO
224:reacts with
171:of the kiln
166:
120:
93:reacts with
75:Cement kilns
74:
73:
52:
36:
34:lead section
1715:K E Peray,
1666:A C Davis,
1478:naphthalene
1384:emissions.
1286:rotary kiln
1246:particulate
1223:→ CaO + CO
1194:During the
1131:exhaust gas
969:endothermic
771:natural gas
645:) and free
492:Hygroscopic
306:rotary kiln
210:), MgO and
161:Cement mill
89:, in which
2069:Categories
1884:2021-05-04
1832:, pp 81-83
1765:, pp 74-75
1761:, Hewlett
1744:, Hewlett
1731:, pp 73-77
1629:2021-05-04
1598:References
1488:As a rule
1014:) and CaO.
961:S + C → C
952:(CCN) as:
936:+ CaO → Ca
775:emissivity
745:Kiln fuels
676:Fuel mills
587:Fuel mills
481:aggregates
479:made with
393:Preheaters
169:combustion
55:April 2021
1966:, pp 76-7
1845:Chapter 4
1807:, p 20.54
1624:0013-0613
1517:Chlorides
1370:marcasite
1215:limestone
1122:pyrometry
1033:sintering
997:quenching
984:, alite,
706:volatiles
559:firebrick
546:sintering
485:amorphous
475:(ASR) in
326:firebrick
295:lime kiln
146:sintering
127:limestone
39:summarize
2080:Concrete
2022:(1997).
1903:Archived
1828:Hewlett
1782:, p. 77.
1581:Thallium
1574:sulfates
1555:vanadium
1314:nitrogen
1175:) and SO
1119:infrared
570:Thailand
477:concrete
231:to form
198:(CaMg(CO
196:dolomite
155:to make
83:portland
1975:Peray,
1587:Mercury
1570:cadmium
1551:arsenic
1494:toluene
1490:benzene
1446:dioxins
1196:clinker
1126:clinker
1028:solvent
914:, or Ca
891:, or Ca
864:Online
658:S → C
598:Coolers
550:melting
465:rawmill
432:cyclone
153:clinker
139:Rawmill
2075:Cement
2053:
2032:
1977:op cit
1964:op cit
1960:op cit
1958:Peray
1875:
1843:op cit
1841:Peray
1830:op cit
1816:Peray
1803:
1793:op cit
1791:Peray
1780:op cit
1776:op cit
1774:Peray
1763:op cit
1759:op cit
1757:Peray
1746:op cit
1742:op cit
1740:Peray
1729:op cit
1723:
1654:
1622:
1559:nickel
1502:xylene
1450:furans
1397:alkali
1366:pyrite
1351:Sulfur
1083:. If
1077:carbon
1073:oxygen
1001:belite
879:belite
630:belite
584:Cooler
532:rawmix
488:silica
444:rawmix
440:vertex
436:vortex
372:slurry
233:belite
186:and Al
157:cement
95:silica
87:cement
2085:Kilns
1993:(PDF)
1167:), NO
902:alite
816:(RDF)
613:alite
528:Japan
265:O·SiO
259:alite
159:(see
135:shale
2051:ISBN
2030:ISBN
1997:IPCC
1873:ISBN
1801:ISBN
1721:ISBN
1652:ISBN
1620:ISSN
1568:and
1566:lead
1506:BTEX
1500:and
1474:PAHs
1448:and
1236:Dust
1219:CaCO
1106:and
759:coal
716:Fans
590:Fans
552:and
173:fuel
131:clay
129:and
1865:doi
1462:PCB
1368:or
1330:+ N
1280:(NO
1268:(NO
1079:to
1009:SiO
990:SiO
940:SiO
932:SiO
923:):
918:SiO
895:SiO
850:EPA
731:STP
712:).
647:CaO
330:oil
261:(Ca
239:SiO
235:(Ca
226:SiO
133:or
2071::
1995:.
1892:^
1871:,
1859:,
1614:.
1557:,
1553:,
1496:,
1492:,
1409:CO
1355:SO
1204:CO
1113:.
1108:SO
1104:NO
1102:,
1100:CO
1098:,
1005:Ca
986:Ca
928:Ca
769:,
765:,
761:,
741:.
490:.
212:CO
194:.
163:).
141:);
2059:.
2038:.
1867::
1696:.
1632:.
1433:2
1425:2
1393:2
1389:2
1382:2
1374:2
1362:2
1357:2
1346:)
1344:2
1334:.
1332:2
1328:2
1301:x
1294:2
1290:2
1282:2
1270:x
1260:)
1258:x
1230:2
1225:2
1221:3
1211:2
1206:2
1200:2
1179:(
1177:2
1171:(
1169:x
1163:(
1135:2
1110:2
1095:2
1093:O
1011:4
1007:2
1003:(
992:5
988:3
982:S
980:3
978:C
965:S
963:3
959:2
957:C
942:5
938:3
934:4
930:2
920:5
916:3
912:2
908:3
906:C
904:(
897:4
893:2
889:2
885:2
883:C
881:(
710:2
660:2
656:3
654:C
643:S
639:2
634:C
632:(
626:S
622:3
617:C
615:(
387:2
267:4
263:3
254:.
252:2
241:4
237:2
228:2
217:.
214:2
208:3
204:2
202:)
200:3
192:3
190:O
188:2
184:2
57:)
53:(
43:.
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
