Co-processing of AFR in Indian cement industry- NCB experiences

Transcription

1 Co-processing of AFR in Indian cement industry- NCB experiences Rabindra Singh, A K Mishra, S K Chaturvedi, Rayees Ahmed and O P Grover National Council for Cement and Building Materials, India 1.0 Abstract NCCBM carried out studies on co-processing of alternate fuels such as MSW, agro waste, plastics & spent wash etc. in various cement plants. During these studies NCCBM checked clinker quality, emission from stacks and physical properties of cement and found to be in acceptable limits. These studies revealed that Co-processing of alternate fuels in cement kilns is technically viable and economically feasible option for treatment of wastes with heat value due to high temperature levels and long residence times in kiln system. 2.0 Introduction India s fragile energy security is under severe pressure from its rising dependence on imported oil/coal, regulatory uncertainty and opaque natural gas pricing policies and poorly developed upstream infrastructure and dependence on fossil fuels as the dominant source of energy in the near future. To meet the growing energy demand over the next few years, India will have to enhance its energy security by procuring energy supplies at affordable prices. Cement manufacturing is an energy-intensive process due to high temperatures required in the kilns for clinkerization. Coal is the predominant fuel burnt in cement kilns. Over the last few years there has been a sharp decline in linked coal to the Indian Cement Industry leading to purchase from open market or coal import at much higher rates. Apart from coal other fuels like petroleum coke, natural gas & furnace oil are also used as fuels in cement kiln. The cement industry has been making continuous efforts over the last few years to enhance the usage of alternate fuels like tyre chips, paint sludge, pharmaceutical waste, plastic waste, MSW, biomass & other industrial by-product having heat value to overcome insecurity in indigenous fossil fuel availability. Practice of using hazardous combustible waste (HCW) as fuel has been evolving and growing over the past two decades in the cement plants of several countries abroad. Though the use of alternate fuels including waste materials containing combustible value it is primarily began for economic reasons, it eventually proved to be more beneficial in relation to ecological objectives in cement industry. Some of hazardous combustible wastes used in the overseas cement plants are waste oils, plastics, refinery sludge, sewage sludge, ETP sludge, etc. In India, spent wash from sugar industry, Pesticide sludges, paint sludge from automobile sector, petroleum refinery sludge, plastic waste etc have been widely attempted along with coal in cement kilns. This paper highlights the findings of case studies on co-processing of alternate fuels and raw materials (AFR) carried out by NCCBM. The paper discusses, the plant trials utilizing different types of waste as alternative fuel and raw materials. 3.0 Co-Processing of Alternate fuels NCB in association of cement plants has been a major partner in carrying out coprocessing trials of a number of combustible wastes as a partial substitute of coal/petcoke in

2 cement plants. Before going for plant trials, availability, characterization, affect on kiln operation & clinker quality besides environment have to be evaluated and for which Techno-economic evaluation should be carried out. Following factors are considered while selecting alternate fuels for co-processing in cement kilns: Variation in characteristics of Alternate Fuel vs Main Fuel in terms of moisture, ash content, net calorific value, volatile content leading to - requirement of feeding in kiln/calciner - proper storage, handling & drying system as required. - Separate feeding & dosing system. Impact on process & machinery like jamming, coating / ring formation, unstable kiln operation, leading to requirement of alkali by pass system, increased air blasters, change of ID fans etc Impact on product quality of clinker with use of alternate fuel 3.1. Procedure of plant trials: Central Pollution Control Board (CPCB) released guidelines for the co-processing of hazardous waste in cement plants in India. According to the guidelines, a cement plant considering co-processing must submit an application for a test burn to the State Pollution Control Board. The SPCB grants test burn permission within 60 days of receipt of the application. The cement plant must then inform the CPCB about the test burn at least 15 days in advance so the latter can monitor the trial run. The test lasts five days starting with a baseline test (with no waste feeding), followed by three days with waste and, finally, on the last day another baseline test is carried out. The test burns are usually conducted with the CPCB, SPCB and a third-party consultant. After successful trials if there is no deterioration in quality of clinker/environment, waste is permitted for co-processing by CPCB/SPCB Methodology: The Guidelines requires detailed reporting of the process, the waste to be used and its manufacturer, all handling and management steps, as well as comprehensive testing of all input and output streams, the clinker quality, and advices to set up a mass balance. Case Study - 1: Co-processing of Spent wash Spent wash is characterized by low ash of about 10% but very high moisture content of 40-50%. Due to low carbon content (~ 20%), the calorific value of the spent wash is significantly low to the tune of kcal/kg (wet) basis. Sulphur in the spent wash is found 0.96% and hence not considered alarming from the point of view of build-ups in the kiln system. The analysis of the spent wash sample indicates the concentration of Na2O at 2.08%, K2O at 3.49% and chloride at 1.54%. The spent wash sample was analysed for various heavy metals covering chromium, lead, nickel, cobalt, zinc, Arsenic, selenium, thallium, cadmium etc. These heavy metals in spent wash are present in small percentages and their presence is unlikely to cause adverse impact on clinker quality and environment. Chlorine is known to enhance the volatility of even low volatile heavy

3 metals. Hence it is imperative that all these heavy metals should be monitored both in clinker and stack gases to assess their impact on product quality and environment. The trial carried out in a cement plant in Karnataka by NCCBM in association with CPCB where spent wash was co-processed in the kiln as a partial substitute of coal. Results indicated that % TSR can be achieved without affecting the kiln operation, clinker quality and cement quality. The clinker quality and physical data of cement during trials are shown in Table 3 and Table 4 respectively. Date Table 3: Clinker quality during trials with spent wash Item, % Day 1 Day 2 Day 3 Day 4 Day 5 LoI SiO Fe2O Al2O CaO MgO SO Na2O -K2O CI Fineness, Blaines (M 2 /kg) Table 4: Analysis of cement during trial of with spent wash Compressive Strength (N/mm 2 ) 1-d 3-d 7-d 28-d Autoclave (%) Soundness Le Chatelier (mm) Setting Time (Min) Initial Final Day Day Day Day Day Case Study-2: Co- processing of CETP sludge CETP sludge is a mixture of fine powder, granules and lumps which has significant and varying amount of moisture (35-50%). On sun drying, the sludge turns from sticky into brittle and non - sticky and becomes soft which is considered suitable for grinding.

4 Proximate Analysis CETP sludge was tested for proximate analysis at NCB laboratory and their results are : Moisture Content -6.1%, Volatile Matter -35.3%, Ash Content % with Ash Content -2.8% and Calorific Value kcal/kg. Ultimate Analysis Ultimate analysis of CETP sludge comprising of Carbon -14.6%, Hydrogen -1.14% and Sulphur -4.9%. Heavy Metals To study the effect of CETP sludge as fuel on the quality of clinker, the heavy metals were determined and results are given in Table 5 Table 5: Heavy Metals in CETP Sludge Sl. No. Constituent ppm (%) 1. Arsenic (As) Barium (Ba) Cadmium (Cd) Cobalt (Co) Chromium (Cr) Copper (Cu) Manganese (Mn) Molybdenum (Mo) Nickel (Ni) Lead (Pb) ND ND 11. Selenium (Se) Strontium (Sr) Zinc (Zn) ND ND Results of CETP trial CETP could be used to the extent of 5% only along with fuels being used by the plant, the impact of above parameters on product quality and environment is least. The laboratory results for chemical analysis, heavy metals in the clinker, stack emissions data, leachability test and kiln parameters indicate that the use of CETP sludge has no adverse impact on clinker quality and environment at present level of CETP sludge addition. However, SO3 content seems to be on the higher side and requires attention to limit the same below the permissible limits of 3.5% in cement. Case Study 3: Co-processing of different types of alternate fuels

5 A cement plant in MP co-processed different type of wastes in its cement kiln. Results of co-processing alternate fuels like RDF, Agro waste & tyre chips, Paint sludge and plastic waste which are non-hazardous and hazardous respectively indicated that there is no significant change in clinker quality as compared to the condition when normal fuel i.e petcoke& imported coal was used. In kiln, 100 % Pet coke was used in the main burner and mix of pet coke (65 %), imported coal (25 %) and alternate fuel (10 %) in the pre-calciner. The results of emission measurements during co-processing of both non-hazardous and hazardous alternate fuels indicated no significant change as compared to the condition when normal fuel i.e. petcoke& imported coal was used. The plant used 17 % AFR & achieved 9.28 % TSR during Ultimate analysis of shredded tyres Element Percentage Carbon Hydrogen 5.94 Nitrogen 1.34 Sulfur 1.89 Zinc 1.50 The following observations are made based on the above analysis of rubber tyres. The sulphur content of tyre is higher compared to coal. Since the percentage of tyre replacement with coal is anticipated to be limited, the sulphur addition into the system is not significant. Since zinc content is present in tyres it will effect the setting time of the cement and based on the trials the fuel substitution may be limited to 25 % (% TSR).the final and initial setting times are increased by 30 sec and 45 sec respectively when coal + chopped tyres are used as a fuel which can be brought down by adjusting the percentage addition of gypsum in cement. There are generally 2 major options for firing of alternate fuels Through main burner pipe In the calciner vessel The essential aspects for the introduction of tyres into the kiln system are The residence time of the used tyres in the kiln system should be sufficiently high so that the waste tyres are fully burned out. Oxygen should be sufficiently available so that complete combustion takes place and there should not be any localized reduction conditions. 4.0 Alternate raw materials NCB has carried out extensive studies on use of alternate materials as blending component of cement for reducing clinker factor thereby reducing energy consumption leading to benefits such as reduced CO2 emissions, conservation of fossil fuels and limestone. R&D

6 activities in the areas of enhanced usage of flyash, slags such as GGBFS, Copper slag, LD slag, low grade limestone and various waste which are byproducts of process industries are being carried out. The results so far are encouraging for reducing clinker factor. The brief description of different ways to reduce clinker factor are summarized below: 4.1. Reducing clinker factor by increased use of fly ash in PPC The increased use of fly ash in Portland Pozzolona Cement (PPC) directly impacts the reduction of clinker factor in cement (clinker factor: % of clinker content by cement mass), thereby reducing CO2 emissions through reduced fuel combustion and reduced limestone calcination. Therefore, exploring newer technical avenues for maximizing the utilization levels of fly ash represents a big challenge and opportunity for CO2 reduction. Fly ash conforming to standard IS: 3812 (1) 2013 can be used (up to 35% maximum) in the manufacture of PPC as per IS: 1489 (part 1) The role of fly ash in PPC is attributed to the pozzolanic action leading to a contribution to strength development. Studies carried out on the Indian fly ash samples have indicated that the range of glass content varies between 15 and 45% and the Lime Reactivity (LR) between 2.0 and 7.0 mpa. The fine fraction of fly ash below 45 micron is a major portion, and contributes predominantly to the performance of PPC. This particular aspect of fly ash is very important with a view to enhance the % of use of fly ash in PPC and concrete and needs further thorough and systematic investigations to arrive at adoptable methodologies of using finer fly ash at higher levels. The quality of the clinker and suitable and adequate admixture addition will improve the fly ash absorption. The addition of plasticizers will help in fly ash absorption in concrete applications. Studies have been undertaken with a view to enhancing lime reactivity of dump ash / pond ash, and fly ash from initial fields of Electrostatic Precipitator (ESP) so that nonconforming fly ash could be made reactive and conform to IS: 3812 (1) 2013 and could gainfully be utilized. These studies have revealed that such fly ash could be utilized up to an average of 25% after activation through mechanical (by screening, fine grinding and separation), chemical (froth flotation, washing with acid and alkalis, and filtration), and thermal (sintering) and electromagnetic routes. The studies on activation of conforming fly ash also indicate that fly ash utilization levels could be increased by about 10-15% from the current levels, subject to revision of national standards. ash). Anticipated benefits Thermal savings: saving potential: 55 kcal /kg cement PPC by increasing fly ash content by another 8 %. Electrical savings: saving potential: kwh/t PPC. Note: The above thermal/electrical savings are calculated considering OPC (95% clinker) as the base level, 27% fly ash or current national average in PPC, and 35% fly ash as the achievable target in future. CO2 reduction (direct): kg CO2/t PPC (for cement with 27-35% by mass fly CO2 reduction (indirect): 1 kwh in specific power consumption reduces CO2 emission by 1 kg hence, reduction in CO2 emission is expected to be 13-17kg/t PPC (for cement with 27-35% by mass fly ash.

7 Note: The above thermal/electrical savings are calculated considering OPC (95% clinker) as the base level, 27% fly ash or current national average in PPC, and 35% fly ash as the achievable target in future Reducing clinker factor by increased use of other materials in making of cement blends Various non-ferrous industries generate industrial wastes that are unutilized, and thus occupy large tracts of valuable land, posing serious environmental and health hazards. Initial studies have shown that these materials have the potential to be used as blending materials at the clinker grinding stage during cement manufacture. This will reduce heat consumption and mitigate CO2 emissions to the extent of the additional levels used. Lead-zinc slag Copper slag Production levels of various types of industrial wastes and by-products of interest Table 6: different types of industrial waste and their availability Industrial waste 'LD' / Blast Oxygen Furnace Slag (BOF) Equilibrium catalyst Jarosite Kimberlite Marble slurry Available quantity 1.0 MTPA 0.8 MTPA 4.0 MTPA 15,000 TPA 0.3 MTPA 0.6 MTPA 5 MTPA Research has been conducted on the technical suitability of these materials for use as blending components and the results are very encouraging, indicating the potential use of leadzinc slag up to 5%, copper slag up to 5%, and equilibrium catalyst up to 15%. As these materials are not included in the Bureau of Indian Standards (BIS) list for use in the grinding stage, they cannot be utilized in the manufacture of cement blends until approved by BIS. However, these above materials along with limestone can be used upto 5% in Ordinary Portland Cement as per BIS Standard. Anticipated benefits Thermal savings: kcal/kg cement blend, depending on the type of blending material. Electrical savings: kwh/t cement blend 5.0 Conclusions & recommendations Co-processing of alternate fuels in cement kilns is one of the most suitable and preferred technologies for energy recovery as it ideally meets the combustion rule of 3 Ts Time, Temperature and Turbulence for effectively destroying the organic portion of the hazardous wastes and chemically integrates the inorganic portion of the wastes in the clinker. Based on trials on co-processing in different plants as stated above it is clear that there is no adverse effect

8 on kiln operation, product quality or emission levels during co-processing in cement kilns. The above case studies clearly demonstrated that there is a need to share the successful practices of Indian cement plants for achieving high TSR among all cement plants. Moreover Cement industry should share international best practices/ R&D and benchmarking with adaptation experiences of multinational companies and leading Indian companies. Co-processing of alternate fuels and raw materials will reduce our dependence on fossil fuels and natural resources. This will help in improving our environment and reducing Greenhouse gas emissions Addition of performance improver upto 5% in OPC is already permitted by BIS. Currently R&D work is in progress for addition of performance improvers in PPC and PSC. Generation of data on completion of study will benefit cement plants. ACKNOWLEDGMENTS The authors have freely drawn upon completed R&D work / status reports of NCB and some of the unpublished work in NCB. This paper is being published with the permission of the Director General, NCB.