Session 3.3 Precalcination
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(2) CemNet Training - Course TCM01. Cement Technology. Module 3 - Session 3. 3.3 Precalcination. At the end of session 3.2 we saw that the increasing thermal loads inflicted on the burning zone, as cement kiln capacities rose, effectively capped long and preheater capacities at ~3000 tonnes per day. Kiln linings with sufficient refractoriness to withstand the burning zone thermal loads involved are not available. The solution to this problem was delivered by precalcination technology. Cement Technology Training. ©2005. Cement Technology. 3. Pyroprocessing. 3.3 Precalcination. In session 3.1 the chemical reactions and thermodynamics of the conversion of raw materials to cement clinker were described. The evaporation of any residual water, dehydration of clay minerals, CaCO 3 calcination and clinker flux formation are all endothermic and consume large amounts of energy. Calcination of the CaCO 3 is the most energy consuming and endothermic of these reactions.. 3000 2000 1000. Cement Technology Training. C3S formation. Clinker flux formation. Deydration of clay minerals. Calcination of limestone. Evaporation of Water. 0 -1000. ©2005. Cement Technology. 3. Pyroprocessing. 3.3 Precalcination. In session 3.1 the chemical reactions and thermodynamics of the conversion of raw materials to cement clinker were described. The evaporation of any residual water, dehydration of clay minerals, CaCO 3 calcination and clinker flux formation are all endothermic and consume large amounts of energy. 3000 2000 1000. Cement Technology Training. C3S formation. Clinker flux formation. Calcination of limestone. Deydration of clay minerals. Evaporation of Water. 0 -1000. ©2005. The solution to the burning zone thermal load problem was to direct the thermal energy input to the point in the kiln where this reaction is taking place, rather than inputing all the thermal energy through the main burner. 3. Pyroprocessing. This document is for the sole use of students enrolled on course TCM01 and cannot be reprinted, reproduced or distributed without prior written consent from Tradeship Publications Ltd © 2005 http://training.CemNet.com. 2.
(3) CemNet Training - Course TCM01. Cement Technology. Module 3 - Session 3. 3.3 Precalcination. A precalcination furnace was added at the base of the preheater. In the in-line configuration shown, the precalcining furnace is installed in the gas riser from the back of the rotary kiln……. …….to the lowest stage of the preheater.. Fuel. 60% of the total kiln fuel requirements are fired in this precalciner, relieving the burning zone of the associated thermal load……. …….and directing the Fuelfuel input to the calcination of CaCO , where the 3 energy is absorbed by the calcination reaction. FL Smidth In-line (ILC) precalciner. Cement Technology Training. ©2005. Cement Technology. 3. Pyroprocessing. 3.3 Precalcination. A precalcination furnace was added at the base of the preheater. As the fuel is being directed to the energy consuming, endothermic, calcination reaction of the CaCO 3 the temperature in the precalciner furnace remains constant between 860~900°C. The endothermic calcination reaction absorbs the thermal energy input in the fuel and prevents the temperature in the precalciner from rising. Fuel. Fuel. FL Smidth In-line (ILC) precalciner. Cement Technology Training. ©2005. Cement Technology. 3. Pyroprocessing. 3.3 Precalcination. A precalcination furnace was added at the base of the preheater. Preheated combustion air is separately ducted to the precalciner from the cooler via the tertiary air duct. Never-the-less the vitiated combustion product gases from the rotary kiln, with their high CO 2, H 2O and N 2 content are also passing through the precalciner.. Fuel. These dilute the oxygen in the tertiary combustion air and suppress the combustion of the fuel in the precalciner. Meaning the precalciner must be Fuel Tertiary combustion air over-dimensioned to ensure adequate burn-out of the fuel. FL Smidth In-line (ILC) precalciner. Cement Technology Training. ©2005. 3. Pyroprocessing. This document is for the sole use of students enrolled on course TCM01 and cannot be reprinted, reproduced or distributed without prior written consent from Tradeship Publications Ltd © 2005 http://training.CemNet.com. 3.
(4) CemNet Training - Course TCM01. Cement Technology. Module 3 - Session 3. 3.3 Precalcination. A precalcination furnace was added at the base of the preheater. These combustion problems in the in-line precalciner configuration were overcome by the development of separate-line precalciner technology. The vitiated exhaust gases from the rotary kiln are directed through their own, dedicated preheater tower.. Fuel. The tertiary combustion air for the precalciner is separately ducted to the precalciner with the calciner combustion products directed to their own dedicated Fuelpreheater tower. Tertiary combustion air. FL Smidth Separate-line In-line (ILC) precalciner (SLC) precalciner. Cement Technology Training. ©2005. 3. Pyroprocessing. Cement Technology. 3.3 Precalcination. A precalcination furnace was added at the base of the preheater. As the precalciner fuel is fired in pure tertiary air with 23% oxygen by mass the problems of poor combustion are eliminated with separate-line precalciner technology.. FL Smidth Separate-line In-line (ILC) precalciner (SLC) precalciner. Cement Technology Training. ©2005. 3. Pyroprocessing. Cement Technology. 3.3 Precalcination. A precalcination furnace was added at the base of the preheater. The necessity for twin preheater towers was overcome by offsetting the precalciner furnace from the gas riser, therefore meaning that the vitiated kiln exit gases do not pass through the precalcalciner. FL Smidth Separate-line-downdraft (SLC-D) precalciner. The tertiary combustion air for the precalciner is Fuel separately ducted to the precalciner.. Fuel. Precalciner fuel is fired in pure, preheated tertiary air containing 23% oxygen by weight. Cement Technology Training. ©2005. 3. Pyroprocessing. This document is for the sole use of students enrolled on course TCM01 and cannot be reprinted, reproduced or distributed without prior written consent from Tradeship Publications Ltd © 2005 http://training.CemNet.com. 4.
(5) CemNet Training - Course TCM01. Cement Technology. Module 3 - Session 3. 3.3 Precalcination. A precalcination furnace was added at the base of the preheater. The necessity for twin preheater towers was overcome by offsetting the precalciner furnace from the gas riser, therefore meaning that the vitiated kiln exit gases do not pass through the precalcalciner. FL Smidth Separate-line-downdraft (SLC-D) precalciner. The combustion products from the precalciner are then drawn down into the gas riser from the kiln. Firing in pure tertiary air and the long residence time of these precalciners makes them particularly suited to low volatile fuels (petroleum coke)., or alternative fuels. Cement Technology Training. ©2005. Cement Technology. 3. Pyroprocessing. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. Long wet cement kilns typically have a length to diameter ratio of 50:1………….. …..and might be supported on 5 or more tyre and roller stations.. L = 50xD. Cement Technology Training. ©2005. Cement Technology. D. 3. Pyroprocessing. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. Long wet cement kilns typically had a length to diameter ratio of 50:1………….. …..and might be supported on 5 or more tyre and roller stations. They can extend to well over 200m in length and have production capacities of 1 million tonnes per year. Although less than 200m in length and production capacities of ~_ million tonnes per year is more normal. Cement Technology Training. ©2005. 3. Pyroprocessing. This document is for the sole use of students enrolled on course TCM01 and cannot be reprinted, reproduced or distributed without prior written consent from Tradeship Publications Ltd © 2005 http://training.CemNet.com. 5.
(6) CemNet Training - Course TCM01. Cement Technology. Module 3 - Session 3. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. Long wet cement kilns typically had a length to diameter ratio of 50:1………….. …..and might be supported on 5 or more tyre and roller stations. Specific production capacity is typically 0.55 tpd/m 3 of the internal volume of the rotary kiln. Exceptionally this specific output might be as high as 0.8 tpd/m 3. Cement Technology Training. ©2005. 3. Pyroprocessing. Cement Technology. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. The feed to a long wet cement kiln is a slurry of the raw materials with >30% water content. Evaporating this water from the slurry is the first process in the rotary kiln. This evaporation consumes ~1000 kJ of thermal energy per kg of clinker increasing the overall thermal energy consumption to 5000 kJ/kg, or significantly higher. Cement Technology Training. ©2005. 3. Pyroprocessing. Cement Technology. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. Heat exchange between the kiln gases and the feed at the back of the rotary kiln is inefficient, and therefore festoons of chains are hung from the inside of the kiln shell to pick up the feed material and promote this heat exchange. These chains typically extend to 70% of the internal diameter of the kiln… ……..… and 30% of the length of the kiln.. Cement Technology Training. ©2005. 0.7D. 3. Pyroprocessing. This document is for the sole use of students enrolled on course TCM01 and cannot be reprinted, reproduced or distributed without prior written consent from Tradeship Publications Ltd © 2005 http://training.CemNet.com. 6.
(7) CemNet Training - Course TCM01. Cement Technology. Module 3 - Session 3. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. Heat exchange between the kiln gases and the feed at the back of the rotary kiln is inefficient, and therefore festoons of chains are hung from the inside of the kiln shell to pick up the feed material and promote this heat exchange. Efficient, well maintained chain systems combined with chemical dewatering agents are required to reduce the thermal energy consumption to 5000 kJ/kg clinker and boost the kiln output to 0.8 tpd/m 3 Cement Technology Training. ©2005. Cement Technology. 0.7D. 3. Pyroprocessing. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. Long dry cement kilns typically have a length to diameter ratio of 35:1………….. …..and again might be supported on 5 or more tyre and roller stations.. L = 35xD. Cement Technology Training. ©2005. Cement Technology. D. 3. Pyroprocessing. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. Long dry cement kilns typically have a length to diameter ratio of 35:1………….. …..and again might be supported on 5 or more tyre and roller stations. They can extend to 160m in length and have production capacities of _ million tonnes per year. Although 300,000 tonnes per year is a large long dry kiln.. Cement Technology Training. ©2005. 3. Pyroprocessing. This document is for the sole use of students enrolled on course TCM01 and cannot be reprinted, reproduced or distributed without prior written consent from Tradeship Publications Ltd © 2005 http://training.CemNet.com. 7.
(8) CemNet Training - Course TCM01. Cement Technology. Module 3 - Session 3. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. Long dry cement kilns typically have a length to diameter ratio of 35:1………….. …..and again might be supported on 5 or more tyre and roller stations. These kilns are particularly suited to desert climates where there was no water available to slurry the raw materials. Thermal energy efficiency is better than long wet kilns as the water in the slurry does not have to be evaporated. Cement Technology Training. ©2005. Cement Technology. 3. Pyroprocessing. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. Long dry cement kilns typically have a length to diameter ratio of 35:1………….. …..and again might be supported on 5 or more tyre and roller stations. Festoons of chains are again used to promote heat exchange between the feed and kiln gases at the back of the kiln. However, as the feed is a dry powder these kilns are prone to high dust losses. Cement Technology Training. ©2005. Cement Technology. 3. Pyroprocessing. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. Long dry cement kilns typically have a length to diameter ratio of 35:1………….. …..and again might be supported on 5 or more tyre and roller stations. Festoons of chains are again used to promote heat exchange between the feed and kiln gases at the back of the kiln. These dust losses adversely impact on the thermal efficiency and productivity of the kilns. Cement Technology Training. ©2005. 3. Pyroprocessing. This document is for the sole use of students enrolled on course TCM01 and cannot be reprinted, reproduced or distributed without prior written consent from Tradeship Publications Ltd © 2005 http://training.CemNet.com. 8.
(9) CemNet Training - Course TCM01. Cement Technology. Module 3 - Session 3. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. Long dry cement kilns typically have a length to diameter ratio of 35:1………….. …..and again might be supported on 5 or more tyre and roller stations. 4900 kJ/kg clinker is the typical fuel consumption, which exceptionally can be reduced to below 4000 kJ/kg with highly efficient chain systems.. Cement Technology Training. ©2005. Cement Technology. 3. Pyroprocessing. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. Long dry cement kilns typically have a length to diameter ratio of 35:1………….. …..and again might be supported on 5 or more tyre and roller stations. Specific productivity of 0.7 tpd/m 3 of the internal volume of the kiln is typical. Exceptionally this can be raised to 0.9 tpd/m 3 of the internal volume of the kiln.. Cement Technology Training. ©2005. Cement Technology. 3. Pyroprocessing. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. The first major innovation away from long kilns was the Lepol process developed by Otto Lelep and delivered by Polysius. These incorporate a drying and calcining chamber before the rotary kiln. The dry kiln feed powder is mixed with ~9% water in a nodulising pan, and the resulting nodules are fed to a travelling grate within the chamber. Cement Technology Training. ©2005. 3. Pyroprocessing. This document is for the sole use of students enrolled on course TCM01 and cannot be reprinted, reproduced or distributed without prior written consent from Tradeship Publications Ltd © 2005 http://training.CemNet.com. 9.
(10) CemNet Training - Course TCM01. Cement Technology. Module 3 - Session 3. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. The first major innovation away from long kilns was the Lepol process developed by Otto Lelep and delivered by Polysius. A travelling grate transports the nodules of kiln feed through the Lepol chamber.. Drying. Calcining. The chamber is divided into drying and calcining chambers. Hot gases from the kiln are drawn successively through the bed of material on the grate passing through the chambers. Cement Technology Training. ©2005. Cement Technology. 3. Pyroprocessing. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. The first major innovation away from long kilns was the Lepol process developed by Otto Lelep and delivered by Polysius. A significant proportion of the thermal work is taken out of the rotary section of the kiln and transferred to the drying and calcining chambers of the Lepol grate. Intimate contact between hot kiln gases and the feed on the grate results in efficient preheating and calcination. Cement Technology Training. ©2005. Cement Technology. 3. Pyroprocessing. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. The first major innovation away from long kilns was the Lepol process developed by Otto Lelep and delivered by Polysius. A significant proportion of the thermal work is taken out of the rotary section of the kiln and transferred to the drying and calcining chambers of the Lepol grate. Thermal energy consumption can be as low as 3200 kJ/kg clinker, although 3750 is more normal. Cement Technology Training. ©2005. 3. Pyroprocessing. This document is for the sole use of students enrolled on course TCM01 and cannot be reprinted, reproduced or distributed without prior written consent from Tradeship Publications Ltd © 2005 http://training.CemNet.com. 10.
(11) CemNet Training - Course TCM01. Cement Technology. Module 3 - Session 3. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. Lepol cement kilns typically have a length to diameter ratio of 25:1………….. …..and are supported on 3 or 4 tyre and roller stations.. L = 25xD. D. Annual capacity in excess of 500,000 tonnes of clinker per year are achieved by the largest Lepol kilns. Cement Technology Training. ©2005. Cement Technology. 3. Pyroprocessing. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. Lepol cement kilns typically have a length to diameter ratio of 25:1………….. …..and are supported on 3 or 4 tyre and roller stations.. L = 25xD. D. Specific output is normally around 2.0 tpd/m 3, and exceptionally might be 2.5 tpd/m 3 or higher. Cement Technology Training. ©2005. Cement Technology. 3. Pyroprocessing. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. Lepol cement kilns typically have a length to diameter ratio of 25:1………….. …..and are supported on 3 or 4 tyre and roller stations.. L = 25xD. D. Taking the preheating and part of the calcination out of the rotary kiln and into the Lepol chamber therefore more than doubled the specific output of cement kilns compared with long kilns. Cement Technology Training. ©2005. 3. Pyroprocessing. This document is for the sole use of students enrolled on course TCM01 and cannot be reprinted, reproduced or distributed without prior written consent from Tradeship Publications Ltd © 2005 http://training.CemNet.com. 11.
(12) CemNet Training - Course TCM01. Cement Technology. Module 3 - Session 3. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. The first major innovation away from long kilns was the Lepol process developed by Otto Lelep and delivered by Polysius. The main problem faced with these kilns are high wear rate and maintenance costs associated with the Lepol grate. These operate with “green” nodules at ambient temperature at the inlet…. Cement Technology Training. 3. Pyroprocessing. ©2005. Cement Technology. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. In the 1950s suspension preheater technology was developed, and this was widely installed from the 1960s. All modern cement kilns incorporate suspension preheaters.. Cement Technology Training. 3. Pyroprocessing. ©2005. Cement Technology. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. Hot exhaust gases from the rotary kiln are drawn up through the successive stages of the preheater tower. Heat exchange between the feed descending the towers takes place in the gas risers between the successive collection cyclones of the preheater.. FL Smidth Suspension Preheater (SP). Cement Technology Training. ©2005. 3. Pyroprocessing. This document is for the sole use of students enrolled on course TCM01 and cannot be reprinted, reproduced or distributed without prior written consent from Tradeship Publications Ltd © 2005 http://training.CemNet.com. 12.
(13) CemNet Training - Course TCM01. Cement Technology. Module 3 - Session 3. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. Hot exhaust gases from the rotary kiln are drawn up through the successive stages of the preheater tower. Feed is alternately lifted into the cyclones, while being preheated, and collected in the cyclones and passed down to the next stage of the preheater. All the preheating and 25~30% of the calcination is again taken out of the rotary section of the kiln.. FL Smidth Suspension Preheater (SP). Cement Technology Training. 3. Pyroprocessing. ©2005. Cement Technology. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. Hot exhaust gases from the rotary kiln are drawn up through the successive stages of the preheater tower. Feed is alternately lifted into the cyclones, while being preheated, and collected in the cyclones and passed down to the next stage of the preheater. Suspension preheaters have virtually no moving parts and therefore eliminated the wear problems of the Lepol grate.. FL Smidth Suspension Preheater (SP). Cement Technology Training. 3. Pyroprocessing. ©2005. Cement Technology. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. Thermal energy efficiency can be boosted by the addition of more preheater stages. Preheater exit gas temperature will reduce by ~30°C for each additional preheater stage, from ~360°C for a 4-stage preheater, to ~330°C for a 5-stage preheater, to ~300°C for a six stage preheater. However, civil costs and pressure drop across the preheater tower rise with each additional preheater stage. FL Smidth Suspension Preheater (SP). Cement Technology Training. ©2005. 3. Pyroprocessing. This document is for the sole use of students enrolled on course TCM01 and cannot be reprinted, reproduced or distributed without prior written consent from Tradeship Publications Ltd © 2005 http://training.CemNet.com. 13.
(14) CemNet Training - Course TCM01. Cement Technology. Module 3 - Session 3. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. We will discuss the design and operation of suspension preheaters further in a later session of the course.. FL Smidth Suspension Preheater (SP). Cement Technology Training. 3. Pyroprocessing. ©2005. Cement Technology. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. Thermal energy consumption of 3500 kJ/kg clinker is typical, although this can be reduced to 3000 kJ/kg clinker in exceptional cases. Specific output of 2.10 tpd/m 3 is typical, although in excess of 2.70 tpd/m 3 can be achieved in exceptional cases.. FL Smidth Suspension Preheater (SP). Cement Technology Training. ©2005. Cement Technology. 3. Pyroprocessing. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. With the addition of precalcining furnaces at the base of the preheater and before the rotary kiln all the thermal work of precalcination has been taken out of the rotary section of the kiln. Typical kiln productivity has risen to over 4.10 tpd/m 3. The length of these kilns has reduced to 70m, or less.. Cement Technology Training. ©2005. 3. Pyroprocessing. This document is for the sole use of students enrolled on course TCM01 and cannot be reprinted, reproduced or distributed without prior written consent from Tradeship Publications Ltd © 2005 http://training.CemNet.com. 14.
(15) CemNet Training - Course TCM01. Cement Technology. Module 3 - Session 3. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. With the addition of precalcining furnaces at the base of the preheater and before the rotary kiln all the thermal work of precalcination has been taken out of the rotary section of the kiln. The space required and footprint of modern precalciner kilns is only _ that of long wet kilns….. ……while, output has been more than tripled to over 10,000 tonnes per day with the largest precalciner kilns. Cement Technology Training. ©2005. Cement Technology. 3. Pyroprocessing. 3.3 Precalcination. Precalcination technology has resulted in a step change in the production capacity of cement kilns. With the addition of precalcining furnaces at the base of the preheater and before the rotary kiln all the thermal work of precalcination has been taken out of the rotary section of the kiln. Some Indian cement companies have been able to boost the output of their kilns to over 7.00 tpd/m 3. We will explore the ways they have done that in succeeding sessions of the course. Cement Technology Training. ©2005. 3. Pyroprocessing. Cement Manufacturing Technology 3. Pyroprocessing – raw mix to cement clinker. 3.3. Precalcination.. Cement Technology Training. ©2005. 3. Pyroprocessing. This document is for the sole use of students enrolled on course TCM01 and cannot be reprinted, reproduced or distributed without prior written consent from Tradeship Publications Ltd © 2005 http://training.CemNet.com. 15.
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