33 Fly ash utilization and rules

Sandeep Jain

epgp books

 

Objectives:

 

1.      To understand the definition of fly ash

 

2.      To gain knowledge on the various sources of fly ash generation, its properties and characteristics

 

3.      To understand the fly ash utilization methods

 

4.      To familiarize the fly ash rules of government of India

 

 

Introduction

 

Coal is a fossil fuel primarily used for power generation. Globally coal reserves have been estimated at over 861 billion tons. India accounts for 286 billion ton of coal reserve other countries with major chunks are USA, China, Australia, Indonesia etc. Coal meets approx. 30.3% of global primary energy needs and generate 42% of world’s electricity. World over, pulverized coal fired boilers are extensively used for power generation.

 

India has fifth largest coal reserves in world, of the total reserves 88% are non-coking coal reserves. In India coal based thermal power plant accounts for about 60% of electricity installed capacity. About 70% of India’s coal production is used for power generation, with the remaining being used by heavy industries like iron & steel & cement industry. The Indian’s coal is characterized by high ash content in range of 30 – 45% in comparison of imported coal with ash content of 10 – 15%. The Indian coal has other useful qualities like low Sulphur content (<0.5%), low iron content, low chloride content & high ash fusion characteristics (Report by CIMFER, 2014). In FY 2015-16, the coal consumption for power plant are 536.64 Million tons. The quantity of ash in coal varies from plant to plant depending on type of coal used, source of supply and also on type of combustion. During FY 2015-16, the coal based power plant installed generation capacity is 145044.8 MW from 151 coal stations and coal consumption was 536.64 Million tons. The average ash content of the coal used in power plants during FY 2015-16 was 32.94%.

 

Primarily the ash is categorized into i) Fly ash, which is very fine material and generic name given to the ash which rise with the flue gases and captured by Electrostatic Precipitators, ii) Bottom Ash, this ash which is coarse in nature and do not fly with flue gas and which is collected from the bottom of the boiler, iii) Economizer / APH ash, its characteristics are very similar to bottom ash and recovered from the Economizer hopper and APH hopper & very small in quantity. Depending upon the source of coal the composition of fly ash & bottom ash vary considerably. The general ratio of fly ash to bottom ash varies between 70 -80 % – 20 – 30%.

 

As per the MoEF notification on November 2009, The term fly ash means and include all ash generated such as ESP ash, dry fly ash, bottom ash, pond ash. Mound ash etc. In FY 2015-16, the total fly ash generation in India was 176.74 Million Ton. This huge amount of fly ash generation creates a problem for ash disposal. The ash disposal requires large land parcels as ash pond, higher amount of water consumption in conventional slurry systems as ash to be kept wet to avoid fugitive emissions, higher cost on energy consumption and maintenance for ash conveyance through pipeline. So the need of hour is to utilize ash instead of disposal. The ash utilization scenario in India as, In FY 1996-97 the ash utilization is just 9.63 % (6.64 Million Ton) which continuously grows up to 60.97% (107.77 Million tons) in FY 2015-16, now a days we are utilizing more than 16 times. (CEA report on fly ash generation, FY 2015-16).

 

Composition – Pulverized fly ash is a residue of coal combustion have fine grained material, mostly of spherical particles which depends on the coal supply source. The fineness of ash is usually measured by 45-micron sieve, in accordance with ASTM method C430 or IS 1727. The specific gravity of fly ash is determined by ASTM C 188 or IS 1727 (for cement). The specific gravity varies with the coal quality.

 

Other physical properties of fly ash like, Fineness – specific surface in m2/kg is in rage of 250 – 270, Particle size as retained on 45-micron sieve – 40 -50, Compressive strength is 85 -90%. The physical properties of fly ash largely depend on the type & operation of coal mill and operation of burner. The fly ash collected from ESP is some greyish white in color, fine particle size, less unburnt carbon (0.25– 0.5%) has good pozzolanic / self-cementing properties so in presence of water can get strength &may solidify while bottom ash is slightly black in color, coarse particle size and higher unburnt carbon (2.5 – 3.5%) having less pozzolanic properties.

 

Table 1 Physical Properties of Fly Ashes

 

The bituminous coal, sub bituminous coal & lignite coals from different mines are substantially different from each other. The fly ash includes substantial amount of Silicon Dioxide, Aluminum oxide and iron oxide and small fraction of other constituents like MgO, Na2O, K2O, chloride, unburnt carbon and heavy metals in traces. The operation & setting of coal mills and their classifiers, operation of burners have great impact on the constituents like unburnt carbon.

 

Table 2 Composition of coal

 

The pozollonic properties of ESP fly ash make it a resource for making cement and other ash based product. The Geo-technical properties of bottom ash, pond ash allow it to use in construction of embankments, structural fills, reinforced fills low lying area development, road construction etc.

 

Utilization of Fly ash

 

Fly Ash is a pozzolanic material which is defined as siliceous or siliceous and aluminous material which in itself possesses little or no cementitious value, chemically react with Calcium Hydroxide (lime) in presence of water at ordinary temperature and form soluble compound comprises cementitious property similar to cement.

 

Fly ash produced in modern power stations of India is of good quality as it contains low sulphur & very low unburnt carbon. As on date most of the new thermal power stations have set up dry fly ash evacuation & storage system to promote ash utilization. In this system fly ash from Electrostatic Precipitators (ESP) is evacuated through pneumatic system and stored in silos. From silos, it can be loaded in open truck / closed tankers. In the ESP, there are various rows depending on the design of ESP. The field at the boiler end is called as first field & counted subsequently 2, 3 onwards. The field at chimney end is called as last field. The coarse particles of fly ash are collected in first fields of ESP. The fineness of fly ash particles increases in subsequent fields of ESP. The fineness increases the utilization of fly ash.

 

The fly ash is further divided into a) Siliceous fly ash which is normally produced from anthracite or bituminous coal and has pozzolanic properties and having reactive calcium oxide less than 10 percent.

 

b) Calcareous fly ash is produced from lignite or sub bituminous coal and has both pozzolanic and hydraulic properties and having reactive calcium not less than 10 percent by mass.

 

During FY 2015-16, a total of 176.74 Million ton of fly ash was generated out of which 107.77 Million tons (60.97%) was utilized by 151 TPPs. Out of 151 TPPs, only 54 TPPS able to achieved the target of ash utilization as per MoEF notification. The 48 TPPS are able to achieved the target of 100 percent ash utilization followed by 37 TPPs achieve as utilization in range of 75 – 100 percent.

 

As far as state wise ash utilization is concerned, the west Bengal has utilized 16.66 Million tons out of 17.53 million tons (95.05%) followed by Maharastra which has utilized 10.48 Million tons out of 17.53 million tons (59.78%). The poor performers are Chhatisgarh which generated 24.23 Million tons of ash out of which utilize only 7.92 Million Tons (32.69%) followed by Utter Pradesh which generated 24.63 Million tons out of which only 11.12 Million tons is utilized (45.15%). Other states like Delhi, Punjab & Haryana although achieve the target of 100 percent ash utilization but their fly ash generation was low i.e. 0.53, 1.91, 5.05 Millio0n tons respectively. The TPPs fall in NCR of near any principle city, the ash utilization increased automatically because of ongoing infra project which utilizes the ash in abundance.

 

Table 3 Sate wise fly ash generation and its utilization during the year 2015-16

 

The fly ash is utilized mainly Cement manufacturing, Mine filling, Ash based brick & tiles manufacturing, Reclamation of low lying areas, Ash dyke raising, embankment in roads & flyovers, Concrete, Hydropower sector, Agriculture & others.

 

In FY 2015- 16, the 43.38 Million tons (24% of total generated) of fly ash is utilized in cement manufacturing, which is very near to ash utilization in FY 2014-15. The cement sector has high potential of ash utilization this opportunity needs to be harvested.

 

Ash based brick & tiles manufacturing is an important area of ash utilization, In FY 2015 -16, 14.76 Million tons (8.35%) of ash is utilized in ash brick/ tile making. The aspect is very important because it also avoid the use of top soil in making clay bricks. The enforcement agencies need to be more stringent & vigilant for implementation of notification & guidelines of utilization of 25 percent ash in brick making.

 

Mine filling is third top area of ash utilization; the abundant mines voids & opencast mines scope of ash filling. In FY 2015-16, 10.33 Million tones (5.85%) ash is utilized in mine filling which is less than the previous year of 13.33 Million tons (13%). This utilization avenue should be taken care with utmost priority because mine filling has high ash utilization potential. The Mine safety department should be taken in confidence for exploring this avenue.

 

A)  In Manufacturing of Portland Pozzolana Cement – Primarily the pulverized coal fly ash is utilized in PPC cement. The Siliceous fly ash has properties which enable it to be use in PPC.

 

As per the IS 3812 (Part 1) :2013 “Pulverized fuel ash – specifications Part 1 for use as pozzolana in cement, cement mortar and concrete” the term pulverized fuel ash is residue resulting from combustion of ground or powdered or crushed bituminous coal or sub bituminous coal. This pulverized fuel ash is divided into two categories Grade 1 for use in cement, mortar and concrete and in lime pozzolana mixture, and for manufacture of Portland Pozzolana cement; Grade 2 for incorporation in cement mortar and concrete and in lime pozzolana mixture.

 

Table 4 Chemical properties of fly ash for requirement in Cement, cement mortar & concrete

Table 5 Physical properties of fly ash for requirement in Cement, Cement mortar & concrete

 

use as admixture in cement mortar & concrete– The pulverized coal ash can also be utilized in admixture in cement mortar & in concrete. The quality of ash utilized for this purpose is governed by IS 3812 (Part 2) 2013. Grade 2 fly ash with lower threshold limit in physical properties can use as admixture in cement mortar and concrete. In one way of utilization is one part of OPC is replaced by fly ash. The disadvantages of this process is that early strength of concrete is lower & higher strength is developed by 50 -60 days after. At later stages the lime which is liberated form hydration of cement reacts with fly ash and contributed towards strength. some fine adjustment with aggregate & water may increase strength in early days also This method of fly ash utilization adopted for mass concrete work where initial strength doesn’t matter. In second way, the fly ash is simply added to the concrete without replacing the OPC. This method provide strength at all ages of the concrete mass.

 

B) In road embankment, flyover & low lying area filling – the bottom ash & pond ash is slightly coarser in nature, it is very good for the road embankment, flyover filling & filling in low lying areas. The statutory authorities also focused on the utilization of ash in national highways. In Easter peripheral way, the ash form Dadri Thermal Power Plant & Badarpur thermal power plant is utilized. It replaces the soil in embankment. The main issue arises is that the availability of ash in proximity. The ash transportation from large distances is costlier become a hurdle in ash utilization.

 

C)  Cenospheres – Cenospheres are lightweight, inert, hollow sphere, filled with air, light grey in colour and mainly made of silica & alumina. Cenosphere get separated from fly ash when fly ash mixed with water, due to light weight the cenosphere float on the surface and can easily accumulated. Large quantity of cenosphere are collected from TPP having conventional wet slurry system for ash disposal. Cenospheres have low thermal conductivity, high electrical insulation, chemically inert, resistance to wear and good sound proof characteristics. These properties make it very valuable material and are used in plastics, polymers, rubber, paints, refractory, automotive composites, aerospace coating, propeller blades etc.

 

D) Use of fly ash in geo polymer and use of bottom ash as replacement of river sand

 

Figure 2 Fly ash utilization

Rules applicable on Ash generation, management & utilization

 

The Indian coal has high ash content in range of 30 – 45%. As large amount of ash is being generated in coal based power plants. This ash needs to be properly utilized or disposed to avoid environment damage. taken care so Various statutory bodies issued statutory & legal requirement time to time for proper handling & utilization of ash. The prominent agency is Ministry of Environment Forest & climate Change (formerly known as Ministry of Environment & Forest), Central Pollution Control board also issued guidelines and the issues is also flagged at NGT time to time.

 

The ash is not covered under Hazardous & Other Waste (Management & Transboundary movement) rules, 2016. In these rules. Schedule I, footnote mentioned that high volume low effect waste like fly ash are excluded from the list of hazardous waste.

 

The statutory bodies frame certain rules & regulations for the coal usages linked with ash percentage, ash utilization management & transportation. MoEF issued notification G.S.R. 02(E) dtd 02 January, 2014 for use of washed / blended or beneficiated coal with ash content less than 34 percent on quarterly average basis by thermal power plant located beyond 500 kms latest by 5th June, 2016.

 

For strengthening the above notification, MoEF & CC issued protocol No. Q-15017/40/2007-CPW dtd 26.08.2015 for sampling, analysis of coal and reporting of compliance for use of coal with ash content less than 34 percent. Protocol highlighted the real time monitoring of ash content in coal by auto mechanical sampler and its location on moving stream at coal discharge points of a conveyor belt to bunker.

 

Initially a notification no. SO 763 (E) dtd 14.09.1999 was issued by MoEF to promote the utilization of fly ash. It gives the target of 100 percent ash utilization for TPP within five years from date of the notification. It says that in 100 km radius of any TPP, at least 25% of fly ash shall be utilized with soil in brick manufacturing and agencies engaged in construction shall have to utilize ash based products & no agency can approve the design the construction of road & flyover with top soil & implementing authority for it is SPCBs & PCCs. A dispute settlement committee is to be set up by TPP for unhindered loading & environmentally sound transportation of fly ash. The notification also says that the filling of mines should be done with at least 25 percent of fly ash. The thermal power plants are free to sell the fly ash to user agencies with certain condition like pond ash should be free, 20 percent of ESP fly ash should be given free to the ash based product manufacturing agencies.

Later a notification no. S.O. 2804(E) dtd 03.11.2009 was issued by MoEF with certain amendments like fly ash termed shall be used for all type of ash like ESP ash, Bottom ash, pond ash, mound ash etc. Herein this notification again pushes the target of 100 percent ash utilization for TPP within five years from date of the notification.

 

MoEF & CC issued a notification no. S.O 254(E) dtd 25.01.2016 regarding ash utilization. In this notification the radius of the ash utilization in brick manufacturing, utilization of fly ash by construction agencies, reclaiming in low lying areas increased form 100 kms to 300 kms of any TPP. The notification also waives off the condition of giving of 20 percent ESP fly ash free of cost to ash brick manufacturer for TPP utilizing 100 percent ash utilization. The ash stock is to be displayed by TPP on web site for ash users. TPP have to provide separate ash silos & access roads to smooth availability of ash to users. For TPP not utilizing 100 percent ash, have to bear entire cost of ash transportation up to 100 kms for ash based product manufacturer or for utilization in soil as conditioner and have to bear 50 percent cost beyond 100 kms to 300 kms. TPPs also have to promote the brick manufacturing plants in vicinity. The notification again relaxes the condition of 100 percent ash utilization up to 31 December, 2017.

 

CPCB issued guidelines for “loading, unloading and nuisance free ash transportation of all type of ash in December, 2013”. The guidelines emphasis on dry collection of fly ash so that same can be used. The current practice of fly ash loading /unloading shall be improved by closing all opening of telescopic chutes to avoid fugitive emissions. The filter attached to chutes should be replaced or cleaned periodically to avoid chocking. The level sensors of the bulkers / silos should be regularly checked to avoid overfilling of ash. The opening of bulkers/ tankers should be closed during ash transportation. Extra precaution should be taken during ash unloading from tankers to silos as leakage may occur from the line. The construction material of silos/ bulkers / filers shall be anti-abrasive material. The bulker shall be cleaned properly before leaving the TPP boundary. The transportation shall be done in closed body tankers / covered with tarpaulin.

 

NGT in a case has ordered dtd 20.08.2015 allowed the use of fly ash in low lying areas, mine filling, road embankment etc as per provisions of the MoEF 1999 & 2009 notifications.

 

Ultimately, the ash should be seen as a resource, as an opportunity rather than a waste or a burden. The other ash utilization avenues should be explored for effective utilization like the ash may be utilized in ceramic, some scientific studies must be done for utilization of fly ash in ceramic products. Some artifacts can be made by utilization of fly ash & can be demonstrate on public places.

 

Summary

 

To summarize, at the end of this module we have studied about

  • Fly ash its definition
  • Sources of fly ash generation
  • Physical and chemical properties of fly ash State wise fly ash generation and utilization Use of fly ash in different preparations
  • Rules governing fly ash

 

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Reference