Adapting with Coal

What is the issue?

• Despite the loosing sheen for coal as a power source, it is unavoidable at least for few decades.
• Given this, the new methodology of power generation with coal gains significance in environmental perspective.

How is coal's importance at present?

• Coal, as a source of energy, is firmly becoming out of favour.
• The climate change considerations have contributed to this change.
• Most countries have plans to phase out coal in the next few decades.
• India has officially announced that it would not set up any new coal-fired power plants after 2022.

Why is coal unavoidable now?

• There is rapid increase in power generation from renewable sources like wind and solar.
• But still, over 60% of India’s electricity is generated in thermal power plants.
• It is estimated that coal would continue to be the mainstay of India’s energy mix for at least three more decades.

How should it be dealt with?

• Efforts are on to ensure that pollution emanating from coal is at least reduced a bit in these intervening years.
• A variety of “clean coal technologies” is being deployed or experimented with.
• The modern “super-critical” power plants also emit lesser pollutants.

How do thermal power plants work?

• Most thermal power plants burn coal to generate heat.
• The heat is used to convert water into steam.
• The pressure of the steam is then used to move turbines that produce electricity.
• The quality of coal is an important factor in deciding the efficiency of the plant.
• It refers to the amount of electricity generated per unit of coal burnt.
• It also takes into account the waste that is released.
• Typically, coal power plants release a lot of carbon dioxide (CO2), a dangerous greenhouse gas.

What is the complexity?

• Coal is cheaply available in India in very large quantity.
• But it is not preferred due to the high ash and low energy content.
• Burning coal in the conventional pulverised mode results in the release of a lot of fly ash.
• This is a major contributor to air pollution and a health hazard too.
• Several techniques in place to capture fly ash, after it is produced, are not very efficient.
• Alternatively, coal is passed through an extensive “pre-processing” process called “washing”.
• The aim is to remove some of the ash content before it is burnt.
• This has also not been very effective.

What is the new finding?

• A new, more effective way of managing the problem ensures that the ash is removed as chunks from the reactor bed itself.
• Also, the procedure reduces the formation of CO2.
• It instead generates synthetic gas (syngas).
• This is a mixture of clean fuel gases like carbon monoxide and hydrogen, as by-products.
• These can then be put to a variety of uses.

How does it work?

• A well-known coal gasification technique is used.
• Here, coal is only partially burnt with a very limited supply of oxygen.
• It is done in the ‘bubbling fluidized bed gasification reactor’.
• At about 100°C, all moisture from the coal is drained out.
• At higher temperatures (300°C - 400°C), gaseous fuels trapped inside coal are released.
• These include gases like nitrogen, methane and a mixture of many other hydrocarbons.
• At temperatures 800-900°C, the carbon in the coal starts reacting with oxygen in the air.
• It also reacts with the steam supplied along with air.
• It then forms carbon monoxide (CO), hydrogen and carbon dioxide (CO2).

How does it help?

• Controlling the amount of air and steam ensures that significant amounts of carbon monoxide (CO) and hydrogen (H2) are formed.
• By this way, production of CO2, which is a greenhouse gas, can be minimized.
• Careful systematic studies have been conducted to arrive at the regime of operation, air to coal and steam to coal ratios.
• It has been found that the addition of steam becomes favourable in the case of high-ash Indian coals.
• In fact, this technique can be extended to produce syngas of high calorific value.
• This can be done by enhancing the oxygen content in the oxidizer.
• Besides, adding biomass, like rice husk along with Indian coal imparts catalytic effect.
• It improves the gasification performance significantly.

What is the way forward?

• The process would improve the attractiveness of Indian coal for use in power plants.
• It could help significantly in the transition period to renewables.
• Existing power plants will have to replace their traditional reactors with gasification reactors for this.
• In Indian coal mine mouths, such gasification reactors can be established to take care of rural power needs.

Source: Indian Express