BROADLY SPEAKING, ALL ASH HANDLING SYSTEMS HAVE THE FOLLOWING SEQUENCE OF PROCESSES:

• Ash handling collection
• Ash Handling System Conveying
• Storage
• Dry or wet out-loading

Depending upon the quantity of fuel, type of boiler, the usability of ash, etc, the right ash handling systems are chosen to ensure the highest efficiency and utilization. Below are different types of boilers that determine the type of ash handling systems that need to be used:

1. Stoker Fired Boilers

Stoker firing is a power-operated fuel feeding mechanism and grate. This self-cleaning system allows for burning large quantities of fuel with ease, gives us greater control over the combustion process with higher efficiency. It also requires less labor of handling ash.

2. Atmospheric Fluidized Bed Combustor (AFBC)

FBC is atmospheric fluidized bed combustion, where the furnace pressure is atmospheric pressure. The combustion exhaust gas from the furnace goes through a cyclone, Bag Filters or ESP for arresting the ash particulates and are let out into the atmosphere. This kind of a system has comparatively lesser residence time, turbulence and lower combustion efficiency and lower desulfurization.

If there is less headspace under the boiler, then a mechanical dry bottom ash handling system is more suitable as it requires no water but still offers continuous ash removal, otherwise pneumatic ash handling may be used to convey ash out into an ash storage silo for interim holding prior to load out for disposal or reuse.FBC is atmospheric fluidized bed combustion, where the furnace pressure is atmospheric pressure. The combustion exhaust gas from the furnace goes through a cyclone, Bag Filters or ESP for arresting the ash particulates and are let out into the atmosphere. This kind of a system has comparatively lesser residence time, turbulence and lower combustion efficiency and lower desulfurization.

3. Circulating Fluidized Bed Combustor (CFBC) Boiler

In Circulating fluidized bed combustion boilers, the furnace is pressurized and the flue gas is re-circulated to capture the unburnt carbon, and to increase the thermal efficiency of the boiler, hence this is the next evolved version of the AFBC. CFBC boilers are particularly suitable for Indian coal as it has a higher percentage of ash than other types. Due to ash recirculation, the unburnt carbon percentage in exhaust gases can be reduced considerably, which in turn increases the quality of ash produced.

All fluidized combustors operate on either mechanical, pneumatic or a combination ash handling system, depending upon the type of fuel used, availability of ash disposal area, and the need for ash utilization.

4. Pulverized fuel Fired Boilers (PF Fired B)

In boilers with pulverized firing systems, about 80% of ash released is fly ash, and the rest gets collected as bottom ash. Since Indian coal has a significantly higher amount of ash, it needs an efficient ash handling system.

5. Waste Heat Recovery Boilers

WHRB boilers recover ‘waste’ heat, generated during the production process by way of fuel combustion or chemical reaction. This heat can be reused by supplementing it with additional heat to raise the boiler inlet gas temperature to a level commensurate with the desired steam conditions.

One of the biggest advantages of WHRB boilers is that they save a substantial amount of primary fuel that otherwise would have been consumed to generate the same amount of steam.

In the early years of thermal energy, coal fired power plants used to dispose-off entire fly ash in slurry form to ash dykes or otherwise, fly ash’s utilization avenues were not available. A few years back development of fly ash’s utilization technologies lead to strict regulations on managing coal-combustion waste to combat pollution and to maximise the applications of fly ash.

Today fly ash is used in so many industrial and commercial applications that it has become a complete industry by itself.

1. BRICK MAKING

Interestingly, a number of technologies are in vogue to manufacture good quality fly ashes bricks.  These are fly ashes-lime-gypsum, fly ash-cement, fly ash mineralization, fly ashes geopolymerization and fly ash-clay bricks, etc.  All types of fly ash bricks except fly ash-clay bricks, do away with kiln firing as well as requirement of clay. Today, India produces over 20 billion fly ash bricks per annum.

One of the best qualities of fly ashes are that it has insulation capability. Since it requires much less heat and energy to manufacture than clay bricks, fly ash bricks are energy-efficient as well as eco friendly. Fly ashes bricks come in several load-bearing grades, and to encourage and ensure consistency of quality, BIS has formulated standards and specifications for all types of fly ashes bricks. According to their official statement, “The standards lay down essential requirements of finish, dimensions, strength, water absorption, etc. in addition to quality of raw materials to be used with a view to achieve quality and uniformity in the manufacture of such bricks.”

2. CEMENT

Fly ashes are a pozzolanic material, it contains silicates & aluminates in amorphous form  and behaves like cement when combined with lime and water. Partial replacement of cement with fly ashes are not only a more viable prospect commercially, it also saves on naturals resources, reduces CO2 emissions and ensures longer durability.

3. ROADS AND EMBANKMENTS

If fly ash cement is used in construction of concrete roads, it reduces the permeability of concrete and also keeps the aggressive expansive minerals from damaging the concrete from the inside. Also, since fly ash is lighter than traditional soils, it causes lesser settlements. It is particularly relevant in stabilization projects and embankments over weak sub-soils.  Further, it exerts lesser pressure on the retaining walls.

4. MINE BACKFILLING

When areas are mined and exhausted, backfilling is required to reclaim that land, otherwise such vast tracts of land will be rendered useless. Since mines require deep or shallow excavation, they leave behind numerous hollows and shafts. If these gaps are not filled in properly, they may open large sinkholes or elongated fractures or other deformations in the future. To avoid such calamities that could possibly affect human lives, it is important to fill the mines with a material that has the ability to fill tight spaces, has a high resistance to water permeation or compression, and is eco-friendly.

Fly ashes has all these qualities and lends itself beautifully as a filler for Mine Void Filling.

5. FLY ASH COAGULANT

Water pollution is one of the biggest ecological concerns today. If on one hand we encourage rapid industrialization, which results in greater production, and therefore more effluents and pollutants, then we must also have measures to manage these wastes so that we are able to reduce our carbon footprint and protect our environment.

Fly ashes has proved useful in Wastewater Treatment, where modified or activated fly ashes traps and adsorbs various types of organic compounds. Textiles, Handmade paper, Tanning & Dyeing etc. are all industries that can benefit from using Fly ash in significantly reducing their contribution towards wastewater.

Indian economy has seen an enormous economic growth in terms of infrastructure development and manufacturing. Given the amount of natural resources that will be used in either creating this infrastructure or in the services provided by them, it is very important that environment-friendly, cost-effective options be considered very seriously. The Fly Ashes handling system industry has received a lot of impetus from the government, but if more and more people are educated about its benefits and enough attention is directed to its positive ecological impact, we are pretty sure that fly ashes will see a lot of research and technological innovation in the coming years.

Across the globe, countries that have presence in coal based plants, and therefore have huge coal ash production, are expressing interest in extracting value out of this potential gold “dust” mine, instead of just dumping it in landfills. India, which ranks 4th in the world in coal ash production, may possibly quadruple the quantum is fly ash generated when it switches to super critical technologies for thermal power. With that situation looming large in our near future, it is critical that countries fast track research on fly ashes utilisation.

Eventually, the choice for finding innovative uses for fly-ashes wins out in the end because not only does one minimize the harsh impact of fly ashes on the soil and ground water, but also helps in recycling an existing, and abundantly available resource that brings commercial benefits too.

Here are some of the ways that countries have found used Of fly ashes :

The use of one tonne of fly ashes replacement in cement production typically saves one tonne of CO2. Perhaps the most important advantage for cement firms, though, is that fly ash is about one-third the price of cement – which is why some cement companies and power plants have entered into joint venture projects to recover fly ash.

A team from the UWC University in South Africa has been trying to completely replace cement with fly ash. Their aim is to create a prototype that can turn fly ash lower-cost roof tiles, bricks, paving stones, building elements like lintels, fire-retardant panels and insulation material, which could offer important solutions in low-cost housing to replace chipboard and gypsum board, or so-called drywall, which are highly flammable. This way, construction material will become cheaper and also result in huge energy savings.

One research from an agricultural university indicates that they have found that a certain composition of fly ash effectively increases yield of some crops and in reclaiming fallow land.

Universities and laboratories in India, South Africa, the USA and Australia etc. alike have been running funded research experiments for extraction of desirable rare earth metals from coal ash like Alumina, Vanadium etc. ‘Beneficiation’ is a term that refers to the process by which carbon is removed from fly ash to produce a higher-value material. Power plants can increase their revenue stream by adding the beneficiation step to their ash handling process.

In South Africa, CSIR researchers are converting fly ash, a by-product of the South African pulp and paper industry, into heat-resistant geo-polymers that can be used in the protection of metal surfaces against high temperatures in furnaces or kilns. The conversion of fly ash into valuable products such as heat resistant geo-polymers offers alternative options that could help the pulp and paper industry to reduce its environmental footprint and waste management costs.

In summary, it does seem that identifying applications of coal ash re-use will be extremely beneficial, offering an enhanced revenue stream for power plants and also be a means of significantly decreasing the carbon footprint.

Fly ash recovery and disposal trends around the world.The World Energy Outlook 2017, Southeast Asia, cited that India, along with other developing economies in Asia, would helm the global demand for coal in years to come. In the next 20 years, power plants are expected to be responsible for almost 75% of the additional coal consumption.

And when there is so much coal, there is of course, a lot of fly ash recovery, coal ash. Globally, the most popular and the most economical solution for coal ash disposal is storage. Cost of disposal plays a big factor and can be curbed to a minimum if there are disposal sites available that are near a power plant.

Considering the ecological impact of coal ash on our environment, almost all countries have developed stringent regulations on its recovery, disposal and usage. In USA for example, the US Environmental Protection Agency (EPA) laid out the first-ever federal rules for coal ash disposal, where America’s coal-fired power plants are required to store coal ash only in landfills and disposal sites that meet minimum structural standards. In China, Fly ash is a Type II Class C general industrial solid waste. Currently, Chinese regulations allow for the fly ash to be stockpiled temporarily if it cannot be comprehensively utilized.

In Germany, where around 10 million tonnes of coal ash is produced per year, around 97% is re-used, and the rest stored only on a temporary basis. Other countries like the Netherlands are doing even better by having a zero landfill policy, which subsequently means that they are required to recycle 100% of the coal ash generated.

In the UK and US, the recent downward market trend in the coal industry has resulted in an increased interest by cement companies in mining landfill storage sites to fly ash recover the ash. There are recent studies and research papers that suggest that fly ash recovery landfills have enormous untapped value and potential that, when unlocked, can bring tremendous ecology-friendly and economically viable opportunities for re-use applications.

In Malaysia, the coal consumption is set to increase by over three times. It already has very stringent pollution targets, therefore it prefers towards using HELE technologies, mainly USC, for new projects. In Vietnam, a recent resurgence of interest in nuclear power could offset coal’s share in the medium-term. “The availability of sufficient capacity from coal plants now being built means that it is only when plants are retired and additional power is needed from 2035 onwards, that AUSC units may be introduced and emissions of CO2 will fall.

WHAT IS FLY ASH?

Fly ash in india : In thermal power plants, when pulverized coal is burned, we get a by-product called Fly Ash. This remnant can be responsible for serious environmental problems if let out incautiously and thus, Macawber Beekay extracts it using Vacuum System or Pressure Conveying System. For years, Fly Ash was considered an industrial waste and a larger part of it used to end up in ash dams & related landfills..

WHY FLY ASH UTILIZATION IS VITAL?

In the last few decades, in energy generation, coal has been a dominant player world-wide and is expected to maintain its dominion in coming years. India shows the largest growth in coal consumption, with over two-thirds of its electricity generation occurring using coal. With a surging utilization, The Indian Ministry of Power estimates that 1800 million tonnes of coal can be used every year leading to generation of 600 million tonnes of Fly Ash by 2030-31.

Loose Fly Ash can lead to severe health and environmental hazards, bringing attention to MoEF’s prescription for plants of achieving 100% utilization. Thus, having made it important to develop technical and economical solutions for fly ash utilization to reduce these fly ash related problems. It is very essential to set-up a Dry Fly Ash Handling System in the power plants.

UTILIZATION OF FLY ASH

The essential idea of reuse of this remnant is not only to control its effects on the environment, but also, to realize economic gain from the sale of this by-product and replace some limited or expensive natural resources with its employment. It can be used in the following areas-

CEMENT MANUFACTURING

Due to the presence of a significant amount of silica, alumina and lime in it, Fly Ash can be used as a sectional substitute (upto 30%) for Portland cement. The inclusion of Fly Ash as the blending material substantially improves the quality and durability of the concrete as Fly Ash reacts like a pozzolana with the lime in cement as it hydrates, creating a sturdy binder. In India, current production of conventional cement is similar to that of Fly Ash blended one. By using Fly Ash based cement, the cement industries can escalate their production with lesser resources.

CONSTRUCTION OF ROAD & EMBANKMENT

Using Fly Ash for road and embankment works gains an upper hand for its gradation, shear strength, compressibility and permeability. It’s also a lightweight material as compared to commonly filled conventional local soil thus, causing lesser settlements. Pozzolanic hardening property gives additional strength to the road pavements/ embankments and decreases the post construction horizontal pressure on retaining walls. It can replace a part of cement and sand in concrete pavements thus making them more economical than roads constructed using conventional materials.

FLY ASH BRICK

Fly ash can be used for manufacturing bricks used for building construction. These bricks are light in weight and stronger than common burnt clay bricks available otherwise. Fly ash can also be used for manufacturing pavement blocks or tiles normally used for strengthening and decorative flooring in pavements, walkways etc. The use of fly ash for manufacturing these will give an economical edge compared to the conventional bricks or blocks and also, help in preserving land area dug out for clay brick manufacturing.

CONCLUSION

The production of coal fly ash is expected to grow for coming years, as a result of the world’s increasing dependence on coal-based power generation. Understanding the characteristics of this by-product provides a foundation for its alternative uses. Having the idea of the diverse ways to use fly ash, such as in the cement manufacturing, road construction etc, is essential to meet the CEA’s guidelines of Fly Ash utilization and its better management to reduce environmental pollution. Macawber Beekay is joining hands with the society for a cleaner and greener India by manufacturing durable Ash Handling Systems..