Title of Invention

A WASTE HEAT RECOVERY AND POWER GENERATION IN CEMENT PLANT AND A PROVESS THEREFOR

Abstract

A waste heat recovery and power generation plant in cement plant comprising boiler and economizers arranged one below the other vertically characterized in that there is provision of a pneumatic cylinder operated three way diverter valve at the entry of the flue gases at the top and screw conveyor being provided at the bottom; steam drum is provided having various safety mountings and controls to collect the steam; steam driven genset and finned type air cooled condenser connected in series condenses steam into hot water, condensate tank is provided to collect said condensate water, this said condensate tank is connected to the above said economizer and boiler by means of piping for resupply of condensate water as feed water; further characterized in that there is p^-ovided a start up boiler to preheat the entire system to about 150°c to avoid condensation in the flue gases.

Full Text

FORM 2 THE PATENTS ACT, 1970 (39 of 1970) COMPLETE SPECIFICATIOIN (Section 10) 'A WASTE HEAT RECOVERY AND POWER GENERATION IN CEMENT PLANT AND A PROCESS THEREFOR' ASHOK DATTATRAYA ATRE, 'Pushpa Heights', l"* floor, Bibwewadi Comer, PUNE-411027 Indian Natioinal The following specification describes the nature of this invention and ttie manner in which it is to be performed. Present invention relates to the waste heat recovery and power generation in cement plant and a process therefor. More particularly, present invention relates to the waste heat recovery and power generation plant in cement plant by - a) Use of medium pressure and / or low pressure steam boilers for heat recovery from gases at about 250°C b) Running steam engine driven gensets (or steam turbine gensets) to produce electrical power c) Condense the steam utilized in gensets by air cooled condensers d) Recycling and reuse of boiler water giving water conservation along with waste heat recovery. In cement plant Rotary kilns and Calciners are used which operate at aroimd 1000°C to 1200'C temperature. The outgoing gases from these equipments are used to heat the incoming feed material and gases are cooled to around 250°C using pre-heater cyclone assemblies. Also the solid material i.e. clinker coming out of the Rotary kiln is also at around 1000°C and is cooled to 100-120°C temperature using ambient air. This also generates hot air of about 220°C. About 60% of the hot air generated is used as combustion air in kiln fiimaces and remaining is exhausted to atmosphere without heat recovery. All these hot gases coming from Rotary kihi, calciner and clinker cooling are cement dust laden. Hence they are passed through Electrostatic Precipitators (ESPs) / Bag Filters before exhausting to atmosphere. Maximum temperature limit for ESP and Bag Filters using economically priced polyester bags is about 140°C. Hence these gases have to be cooled from 250°C to 140°C by evaporation cooling by passing it over water spray. This leads to wastage of this heat as well as loss of water to atmosphere. The evaporated water also increases mass of the air being fed to ESP, requiring larger size of the ESP. Thus a huge amoimt of heat and water is being wasted in the present cement plants. A novel heat recovery and power generation system has been designed usmg heat from exhaust gases of Rotary kiln and clinker cooler. Following issues need to be addressed while designing waste Heat Recovery in Cement Plant. 1. Methods of avoiding Deposition of Cement Powder on the Heat Transfer Surface which otherwise results in fouling and lesser heat recovery. 2. Methods of dislodging deposited dust and keep the heat transfer surface free of dust. 3. Avoid exposure of the flue gases to cold surface of the equipment during start¬up or interruptions. This results in condensation of the flue gas moisture and when this moisture comes in contact with the cement powder, cement gets "set" on the surfaces which is difficult to remove. Hence slow build-up of such patches results in chocking of the system. 4. Availability of the water and its appropriate utilization to conserve the water by designing the system judiciously. 5. Selection of appropriate electrical power generation system to maximize the power generation. 6. Bringing down the flue gas exhaust temperature to sufficiently low level, so that less expensive method of Gas cleaning (after Heat Recovery) of cement powder separation from flue gases can be utilized. 7. Keep flue gas pressure drop in boiler low. 8. Utilize the vertical elevation available (due to preheater Cyclones already existing) while configuring boilers. 9. Easy removal of cement dust separated in boiler. 10. Automatic diversion and bypass of hot gases to gas washer / cooler in case of boiler safety / abnormal boiler working conditions. 11. The system engineered should have attractive payback periods satisfying the investment criteria. Heat Recovery from the Cement Plant hot exhaust is a difficult issue because of the following problems faced - a) Design which satisfies various objectives simultaneously (mentioned above in point 1 to 11) is not available. b) These gases have lot of cement dust which gets deposited on the heat recovery surfaces causing lot of fouling. c) If gases are cooled below dew point, water condenses and comes in contact with the cement forming hard mass on the equipment surface. This results in chocking of the system subsequently, resulting in lower heat recovery. d) Lot of water is wasted in cooling the gases before they are sent to ESP. Normally cement plants are in arid areas. Hence availability of water is scarce especially during summer. Increasing population is further creating higher priority for use of scarce water for domestic purposes and water may not be available for cement industry. e) Recovering the heat and using it other than electrical power generation was not done, since heat recovery boiler designs at 250°C gas temperature or lower are not available. The object of the present invention aims at developing a process and a plant for waste heat recovery and power generation in cement plant. It is also object of the present invention to recycle and re-use of boiler water giving water conservation along with waste heat recovery. According to this invention, therefore, a waste heat recovery and power generation plant in cement plant comprising boiler and economizers arranged one below the other vertically characterized in that there is provision of a pneumatic cylinder operated three way diverter valve at the entry of the flue gases at the top and screw conveyor being provided at the bottom; steam drum is provided having various safety mountings and controls to collect the steam; steam driven genset and finned type air cooled condenser connected in series condenses steam into hot water, condensate tank is provided to collect said condensate water, this said condensate tank is connected to the above said economizer and boiler by means of piping for resupply of condensate water as feed water, furflier characterized in that there is provided a start up boiler to preheat the entire system to about 150°c to avoid condensation in the flue gases. The invention is described with reference to the accompanying drawing wherein fig.l shows plant layout of waste heat recovery and power generation plant in cement plant according to the invention. Now referring to the figure of the accompanying drawing the basic system consists of water tube type boiler (1) and economizer (2) arranged one above the other vertically which allows downward moment of the flew gas from top to bottom. A pneumatic cylinder operated three way diverter valve (3) is fitted to the entry point of the hot gases above the said boiler (1). The hot gases enter the system from the top and move downwards. Velocity of the gases is kept lower so that cement powder separates by gravity and pressure drop across the system remains minimum saving air blower power. The "Co-current down flow arrangement" for air and cement powder greatly enhance the movement of separated cement powder to the lower portion without accumulation or deposition in the system, minimizing / eliminating fouling or chocking. The gravitational flow of the powder also eliminates additional power requirement for its conveying. Screw conveyor (4) is provided at the bottom of the system to remove the separated cement powder, reducing the dust load on ESP or Bag house. The steam generated in the boiler (1) is stored in a steam drum (5) having various safety mountings and control. From the said steam drum (5) the steam is supplied to the steam engine driven genset (6) to generate electrical power. Operation of the said steam engine (6) is sensed by a speed sensor (ss) provided therein. Back pressure on the steam engme is kept slightly above the atmospheric pressure. Steam exhausted from the said steam engine (6) is condensed in a finned type air cooled steam condenser (7). A cooling air fan (10) is provided to the said finned type air cooled steam condenser (7). Speed of the said cooling air fan (10) is controlled by monitoring condenser inlet pressure through a pressure fransmitter (PT) and variable speed drive (11) provided therein. The condensed water from the said finned type air cooled steam condenser (7) is stored in the condensate tank (8) and re-supplied to the said economizer (2) as feed water. Thus water circuit forms a closed loop conserving lot of water and also eUminates need of large capacity elaborate water softeners which other wise would have been necessary for input water treatment. The said condenser (7) also is selectively kept air-cooled and not watef cooled type to minimize the use of water in the cement plant. In steam based power generation Steam Engine (6) is preferred to Steam Turbine since Steam Engine is much more efficient and generates almost double the power as shown by calculations fiimished later. Condensation of moisture in the flue gas will endanger the system. Since that water when comes in contact with the cement powder will form the hard mass on the tube surface causing fouling / chocking of the system. Hence the flue gas temperature should always be kept above the dew point. Hence for cold start or during any interruption in the Heat Recovery Boilers, steam is supplied to the system by a start-up boiler (9) to keep the temperature at the required level avoiding condensation in the flue gases. The system is automatic. It senses temperature & pressure inside the boiler & steam admission is initiated from 'start up' boiler. This said start up boiler (9) can be Gas / oil fired and draws input water from the said condensate tank (8) itself In the said condensate tank (8) arrangement is also made for soft water inlet. Details of components in the figure 1: - Boiler (1) Economizer (2) Three way diverter valve (3) Screw conveyor (4) Steam drum (5) Steam engine based electrical power genset (6) Finned type air cooled condenser (7) Condensate tank (8) Start up boiler (9) Cooling air fan (10) Speed sensor (ss) pressure transmitter (PT) variable speed drive (11) Operation of the plant: - The hot gases enter the system from the top and move downwards. The waste heat recovery takes place in boiter and economizer. Velocity of the gases is kept lower so that cement powder gets separated by gravity and removed by screw conveyor. The generated steam is stored in the steam drum, which is supplied to the steam engine, which acts as prime mover for electrical power genset. The exhaust steam from steam engine is fed to the finned type air-cooled condenser and the condensate is stored in the condensate tank, which is supplied to the economizer as input water. The start up in cold start condition, economizer and boiler are preheated by steam generated by separate start up boiler to heat the system to required minimum temperature. With only medium pressure boiler &economizer Waste Heat Recovery for a typical cement plant of 4500 Tons Per Day capacity estimated savings/ earnings will be as given below - Safeties and Interlocks : A) A pneumatic cylinder operated "Three way diverter valve is fitted on the entry point of the hot gases and the hot gas passage is automatically diverted to the water spray tower in the following cases - 1) Waste Heat Recovery Boiler / economizer temperature is lower than the required level. 2) The flue-gas temperature at the inlet is lower than the required temperature. 3) The steam pressure in the steam drum is out of the desired upper and lower Hmit. 4) Boiler water level is low. 5) Boiler feed pump trips. 6) Steam pressure of start up boiler lower than desired. 7) Power supply to cogen plant is OPF. B) Operation of the steam Engine is sensed all the time by a speed sensor. In case the engine stops, a control valve in the by-pass line opens diverting the steam directly to the air-cooled condenser. C) A pressure transmitter senses the input pressure to the air-cooled condenser keeping constant back pressure on the steam engine. It also gives signal to the variable speed drive of the condenser blower. This controls the blower rpm of the air-cooled condenser to the desired level, conserving electrical power & also avoiding excessive cooling of the condensate water. D) Functioning of low temperature safety (Start-up Boiler) : To prevent the contact of flue gases with low temperature metal surface, this Safety is incorporated. This avoids condensation of water vapour in flue gases andresultanthardmassformationofcement powder and water. A start-up boiler is always kept at about 140 °C. as standby or "Banked Position". Whenever the flue gas flow is stopped, waste heat recovery also will not take place. The steam pressure in the steam drum will drop operating the pressure switch PS2. This controls following three functions : 1. Control Valve at the start-up boiler main steam outlet is opened which supplies steam to the Economizer and Main Boiler. 2. 3 Way Valve between Economizer and Boiler operates and supphes the steam to the Ejector which also draws high temperature water from the steam drum to heat the boiler tubes. 3. The control valve between the Economizer and Boiler which is on the opposite side of the 3 Way Valve also opens and supplies start-up boiler steam to the Main Boiler Tubes. Thus in no case the system temperature is allowed to drop below the desired level avoiding water condensation and chocking of the flue gas path. To sum up following advantages are achieved. 1. Low pressure drop on the flue-gas, conserving fan power. 2. Flue gas and dislodged cement dust, both move in the downward direction resulting in the self-cleaning process. 3. Dust deposition and fouling being avoided, heat transfer effectiveness is ensured. 4. Provision of start-up boiler & automatic instrumentation avoids cold-start and condensation problems. This fiirther eliminates the possibility of chocking of the system. 5. Automatic diverter valve at the flue gas entry gives improved safety on system chocking and over heating of the system. 6. Start up boiler is always at 140 °C minimum i.e. in " Banked Position" to keep the system at 140 °C min., even in case of flue gas flow failure. 7. Closed loop water system conserves huge amount of water. Also it eliminates the need for large capacity water softeners which otherwise would have been necessary for boiler feed water. 8. Electrical power generated gives additional earnings to make the system viable. Conservation of water Tremendous quantity of water is conserved due to following: 1. Cooling of hot gas in Waste heat recovery boiler , drastically reducing the quantity of water required in spray tower. 2. Use of low pressure cooling the gas to 140 °C, eliminating the need for spray tower 3. Closed loop water circuit facilitating use of condensed water. 4. Use of finned type air-cooled condenser instead of water-cooled condenser. I CLAM: 1. A waste heat recovery and power generation plant in cement plant comprising boiler and economizers arranged one below the other vertically characterized in that there is provision of a pneumatic cylinder operated three way diverter valve at the entry of the flue gases at the top and screw conveyor being provided at the bottom; steam drum is provided having various safety mountings and controls to collect the steam; steam driven genset and finned type air cooled condenser connected in series condenses steam into hot water, condensate tank is provided to collect said condensate water, this said condensate tank is connected to the above said economizer and boiler by means of piping for resupply of condensate water as feed water; further characterized in that there is provided a start up boiler to preheat the entire system to about 150°c to avoid condensation in the flue gases. 2. A plant as claimed in 1 wherein the boiler and the economizer is water tube type with tubes hanging vertically, water is inside the tube and flue gas outside the tube. 3. A plant as claimed in claim 1 and 2 wherein the said steam engine is provided with speed sensor to sense the operation. 4. A plant as claimed in claim 1,2 and 3 wherein the pressure transmitter and variable speed are provided in between the steam engine and finned type air cooled condenser to sense the input pressure of finned type air cooled condenser. 5 A plant as claimed in claims 1,2,3 and 4 wherein the said finned type air cooled steam condenser is provided with air cooling fan. 6. A plant as claimed in claims 4 and 5 wherein the speed of cooling air fan is controlled by monitoring condenser inlet pressure through a pressure transmitter and variable pressure drive. 7. A process for waste heat recovery and power generation by using the plant as claimed in 1 to 6 comprising the steps of a) entering the flue gases in the system from the top and move downwards and generating the steam in boiler and economizer, b) the said generated steam is collected in the steam drum and supplying the steam to the steam engine which acts as prime mover for electrical power genset, c) feeding the exhaust steam from steam engine to the finned type air-cooled condenser and storing in the condensate tank which is supplied to the economizer as input water. 8. A waste heat recovery and power generation plant in cement plant as claimed in claims 1 to 7 and as herein described with reference to the figure of accompanying drawing. Dated this 31st Day of May, 2001 M.D.BHATE AGENT FOR APPLICANT

Documents:

545-mum-2001-abstract(27-8-2004).doc

545-mum-2001-abstract(27-8-2004).pdf

545-mum-2001-abstract(granted)-(17-1-2006).pdf

545-mum-2001-cancelled page(27-8-2004).pdf

545-mum-2001-claim(27-8-2004).pdf

545-mum-2001-claims(13-6-2001).pdf

545-mum-2001-claims(27-8-2004).doc

545-mum-2001-claims(granted)-(17-1-2006).pdf

545-mum-2001-correspondence(27-8-2004).pdf

545-mum-2001-correspondence(ipo)-(17-2-2006).pdf

545-mum-2001-correspondence(ipo)-(29-8-2003).pdf

545-mum-2001-description(complete)-(13-6-2001).pdf

545-mum-2001-description(granted)-(17-1-2006).pdf

545-mum-2001-drawing(13-6-2001).pdf

545-mum-2001-drawing(27-8-2004).pdf

545-mum-2001-drawing(granted)-(17-1-2006).pdf

545-mum-2001-form 1(13-6-2001).pdf

545-mum-2001-form 16(13-7-2009).pdf

545-mum-2001-form 19(9-6-2003).pdf

545-mum-2001-form 2(complete)-(13-6-2001).pdf

545-mum-2001-form 2(granted)-(17-1-2006).pdf

545-mum-2001-form 2(granted)-(27-8-2004).doc

545-mum-2001-form 2(granted)-(27-8-2004).pdf

545-mum-2001-form 2(title page)-(complete)-(13-6-2001).pdf

545-mum-2001-form 2(title page)-(granted)-(17-1-2006).pdf

545-mum-2001-general power of attorney(13-7-2009).pdf

545-mum-2001-power of authority(13-6-2001).pdf

545-mum-2001-specification(amended)-(27-8-2004).pdf

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