Global Energy Trends in Alumina Refinery

Transcription

1 16 th Dec 2016 Global Energy Trends in Alumina Refinery N N Roy

2 World Alumina Production

3 World Alumina Production

4 Alumina Refining Fuel Consumption 2014 AFRICA & ASIA (EX CHINA) CHINA NORTH AMERIC A SOUTH AMERICA EUROPE OCEANIA WORLD REPORTED COAL OIL GAS ELECTRICITY OTHER

5 Energy Consumption in Alumina Refinery Enormous emphasis is placed on the specific energy consumption for the refining of Alumina from Bauxite. The current spared of specific energy consumption of the industries varies from 8 GJ/t to 22 GJ/t (for Bayer refineries) Energy consumption is highly technology specific with Digestion & Calcination accounting for 60% of refinery thermal energy consumption The energy required by the Bayer Process is very much dependent on the quality of the raw material, with böhemitic or diasporic bauxites requiring higher temperature digestion, often associated with a higher fuel input. Mining of the Bauxite requiring electrical energy & fuel oil for transportation Conveyors requiring electrical energy Crushing & Grinding requiring electrical energy Desilication area requiring steam & electrical energy Digestion area requiring steam & electrical energy Evaporation requiring steam & electrical energy Hydrate washing/filtration requiring steam & electrical energy Red mud washing/disposal requiring steam & electrical energy Calcination area requiring fuel oil & electrical energy

6 Theoretical Energy Requirement to Produce Alumina The theoretical energy requirements to produce alumina from bauxite are quite modest, the main chemical reactions that take pace are: Dissolution of gibbsite or boehmite in digestion (endothermic) Dissolution of kaolinite and the re-trasformation in to sodalite based de-silication products (endothermic) The precipitation of gibbsite (exothermic) The calcination of gibbsite to smelter grade alumina (endothermic) Lab studies shows that the theoretical energy requirement to produce 1 tone of alumina is only ~2 GJ/t So why actual energy is so high from theoretical????? There are pre-existing thermal requirements for these reactions to take place to begin with, for example the dissolution of gibbsite or boehmite requires relatively high temperature and concentration of caustic, this means that large volumes of inert material need to be heated from which heat may or may not be recovered and large flows requires large vessels, heat exchangers and equipments that also incur relatively large heat losses.

7 Energy Requirement: Bayer & non Bayer Refineries The average energy consumption for all the refineries is ~13.8 GJ/t of calcinaed alumina with a range from 8 GJ/t to 43 GJ/t The average energy consumption for Bayer refineries is ~12.5 GJ/t and ranges between 8 GJ/t to 21.9 GJ/t Those refineries that uses some from of sinter, Bayer sinter or alumina extraction from non bauuxitic ore have an average energy consumption of ~22 GJ/t ranging from 14 to 43 GJ/t

8 Effect of Refinery Technology of Energy Consumption The effect of digestion technology (LT & HT) on energy consumption of 19 known refineries shows: Although, on average, low temperature refineries uses less energy than high temperature ones, however, The large standard deviation in refineries using high temperature digestion reveals there are cases of high temperature refineries having lower energy consumption than refineries using low temperature digestion technology

9 Alumina Refining Energy Consumption

10 Alumina Refining Energy Consumption

11 Worlds Energy Consumption Distribution Africa & Asia (Excluding China) South America Australia North America China & Europe

12 Worlds Best Energy Consumption

13 Steps taken to Reduce Energy Consumption Bauxite Quality and Liquor Productivity The high content of available alumina results in low specific bauxite consumption. this is beneficial in terms of energy utilization, since the amount of non gibbsite fraction of bauxite, which does not contributes to the production of hydrate, is small. Heat loss through bauxite residue is relatively low due to low bauxite residue factor (mass of mud per mass of alumina produced) due to high available alumina content The content of organics in the bauxite is very low, results in very low impurities in the plant liquor. The spent liquor analysis shows, the concentration of organic carbon, sulfaet and oxalate are low and causticity of liquor is very high. The plant is operated with a high caustic concentration and the precipitation productivity of 89 gpl is achieved. Bauxite residue is filtered in a DF and disposed at high solids. The water collected from RDA is neutralized and clarified in water treatment solutions and realized as a effluent in river There is no water running from RDA to process. This approach avoids the contamination of plant liquor with additional impurities and contributes to maintain clean liquor with high liquor productivity. Liquor impurities are purged from the process with bauxite residue

14 Steps taken to Reduce Energy Consumption Heat Integration The pregnant liquor stream is expanded and flashed in 5 stages from digestion temperature and pressure to atmospheric condition. The liquor is released from blow-off tank at a temperature close to liquor boiling point. The difference in heat sink and source is very small and hence heat loss to atmosphere from blow-off tank is very less. Direct steam injection, increases the difference between heat source and heat sink in digestion, an additional amount of water must be evaporated and requires additional energy. Also the caustic concentration drops due to dilution with steam and at lower caustic concentration less bauxite can be changed to the liquor and liquor productivity decreases. Indirect heating of the bauxite slurry is another important contributor to low digestion steam consumption Better performance of vacuum flash cooling unit resulted in higher spent liquor temperature and finally reduced the live steam in digester and improves the performance of evaporation unit. Spare vacuum flash cooling unit is installed so that cleaning and maintenance can be performed without any major performance losses

15 Steps taken to Reduce Energy Consumption Water Balance The water balance directly affects the energy utilization of an alumina refinery. It is unavoidable that, water from different sources dilute the plant liquor. With the higher rate of water dilution the demand for evaporation increases and at the same time energy used in the form of live steam With high liquor productivity and no direct steam injection dilution of liquor with water is very minimum Main sources are: moisture from bauxite, water for mud and hydrate washing, water with caustic, lime slaking, gland water and some dilution. Regenerative condensate is used for mud and hydrate washing Dilution of plant liquor with other sources such as rain, water hosing and gland water is moderate

16 Energy Consumption with Different Technology:

17 Energy Saving Potential in Alumina Refinery Regular checking of input and output size of primary, secondary and ball mill discharge granulometry Replace the existing worn out internal lining of the ball mill by high chromium steel lining Optimizing grinding media specifically sizing of the balls to obtain better performance which will reduce specific energy consumption Optimise residence time based on silica in liquor by increasing solids concentration and raising temperature Go for indirect steam heating instead of direct steam injection Post Desilication will always cause larger steam consumption as well as auto precipitation of alumina Proper descaling of flash tanks Proper condensate recovery Optimize electrical energy for running the disc and drum filters, vacuum pumps etc Reducing un-authorised dilution in hydrate filtration area Proper maintenance schedule for cleaning of calendria / evaporator tubes

18 Effect of Refinery Technology on Energy Consumption Many improvements have been made on Bayer energy consumption over the years such as: - Improved de-scaling methods - Chemical scale inhibiters - Falling film evaporators - Improved yield in precipitation - Increased no of flash stages in digestion and evaporation The largest energy consumers are Digestion, Calcination and Evaporation in this specific order. Selection of technology such as single stream digestion, circulating fluidized bed calciner and falling film evaporator can have significant impact of energy consumption The substitution of wash water with red mud filtrate by using filter press technology, leaves the option of either reduce evaporation requirements or elimination of evaporation plant together The optimization of concentration system in the Bayer cycle, especially reducing the concentration difference between pregnant liquor and evaporated spent liquor is very important to reduce energy consumption The equipment with higher heat efficiencies, better heat recovery and less heat losses should be applied for the greatest energy savings With all this change in technologies plant are. Pushing towards less than7 GJ/t mark

19 Muri Best Practices Use of sodalite scale inhibitor in High temperature liquor heaters resulting in average ~ 70 days life with constant heat transfer coefficient 75% evaporator house condensate to boiler house resulting in lower auxiliary steam consumption (upto 3 effect condensate send to boiler ~ 100 m3/hr) PHE installation to heat feed liquor from excess heat of condensate to improve steam economy by ~ 0.25 t/t Pushing towards less than7 GJ/t mark

20 Thank you

21 Energy Consumption in Alumina Refinery Average Power Labour Productivit Baux:Ala Caustic Loss Bayer Circuit Calc. Fuel Cons. y Total Fuel Refinery Ratio (t/t) (kg/t Ala) (GJ/t) Fuel Type (GJ/t) Fuel Type (kwh/t) (Man-hrs/t) (GJ/t) AFRICA Friguia Oil 5.6 Oil ASIA Belgaum Oil 4.3 Oil Damanjodi Coal 2.9 Oil Lanjigarh Coal 3.0 Oil Muri Bihar Coal 3.3 Oil Renukoot Coal 3.3 Oil AUSTRALASIA Gove Oil 3.1 Oil Kwinana Gas 2.6 Gas Pinjarra Gas 3.1 Gas QAL Coal 3.0 Gas Wagerup Gas 3.0 Gas Worsley Coal 3.1 Gas Yarwun Coal 3.3 Gas SOUTH AMERICA Aluminio (Sorocaba) Oil 3.1 Oil Alunorte Gas 3.0 Gas Pocos de Caldas Gas 3.1 Gas Sao Luis Oil 2.7 Oil Clarendon Oil 3.5 Oil Ewarton Oil 4.1 Oil Paranam Coal 3.0 Oil Bauxilum Oil 3.1 Oil

22 Energy Consumption in Alumina Refinery Average Power Labour Baux:Ala Caustic Loss Bayer Circuit Calc. Fuel Cons. Productivity Total Fuel Refinery Ratio (t/t) (kg/t Ala) (GJ/t) Fuel Type (GJ/t) Fuel Type (kwh/t) (Man-hrs/t) (GJ/t) CHINA Chiping Xinfa Coal 3.3 Gas Chongqing Chalco Coal/Gas 3.2 Gas Guangxi Huayin Coal 3.2 Gas Guangxi Jingxi Coal 3.0 Gas Guangxi Pingguo Coal 3.0 Gas Guizhou Coal 3.1 Gas Guizhou Qingzhen Coal 3.2 Gas Guizhou Qiya Coal 3.3 Gas Guizhou Zunyi Coal 3.3 Gas Henan Huiyuan Coal 3.3 Gas Henan Xiangjiang Wanji Coal 3.2 Gas Henan Yixiang Coal 3.8 Gas Henan Zhongmei Coal 3.3 Gas Lubei Chemical Coal 3.3 Gas Nanchuan Xianfeng Coal 3.3 Gas Pingba Hongda Coal 3.8 Gas Sanmenxia East Hope Coal 3.2 Gas Sanmenxia Kaiman Coal 3.2 Gas Shandong Coal 2.6 Gas Shandong Nanshan Coal 3.3 Gas Shandong Weiqiao Coal 3.2 Gas Shanxi Coal 3.3 Gas Shanxi Jiaokou Coal 3.3 Gas Shanxi Liulin Coal 3.4 Gas Shanxi Xiaoyi Tianyuan Coal 4.9 Gas Shanxi Xiaoyi Xingan Coal 3.3 Gas Shanxi Yangquan Coal 3.3 Gas Shanxi Yuanping Coal 3.3 Gas Tuoketuo Datang Coal 3.2 Gas Yunnan Wenshan Coal 3.2 Gas Zhengzhou Coal 3.0 Gas Zhongzhou Coal 3.1 Gas

23 Energy Consumption in Alumina Refinery Average Power Labour Productivit Baux:Ala Caustic Loss Bayer Circuit Calc. Fuel Cons. y Total Fuel Refinery Ratio (t/t) (kg/t Ala) (GJ/t) Fuel Type (GJ/t) Fuel Type (kwh/t) (Man-hrs/t) (GJ/t) CIS Ganja Coal 5.8 Oil Pavlodar Coal/Gas 3.9 Gas Achinsk Coal/Gas 5.2 Gas Bogoslovsk Oil 4.8 Oil Uralsky Coal/Gas 3.4 Gas Nikolayev Coal/Gas 3.9 Gas EUROPE Birac Oil 2.7 Oil Gardanne Gas Gas Distomon Gas 3.9 Oil Aughinish Gas/Oil Tulcea Gas 4.3 Gas Coal/Gas/ San Ciprian Oil MIDDLE EAST Jajarm Gas 4.7 Gas Seydisehir Gas 1.3 Gas/Oil NORTH AMERICA Arvida Gas 3.3 Gas Burnside Gas 4.2 Gas Corpus Christi Gas 2.5 Gas Gramercy Gas 3.6 Gas Point Comfort Gas 2.7 Gas