While the world grapples with the problem of climate change, it is also necessary to bring down CO2 emissions and pollution levels in 90 cities, which account for a third of the emissions. These emissions are mainly caused by automobile transportation and have exposed a quarter of the population living in these cities to health risks due to tailpipe emissions.

Twin Goals: Cleaner Vehicles, Greener Power

This project is one of the pathways to achieve the twin universal objectives of lowering tailpipe emissions from vehicles and reducing CO2 emissions from power plants, which account for 75% of global greenhouse gas (GHG) emissions. Diesel blended with 20% DME has near-zero particulate emissions and a heat value of 39 Mj/Kg, compared to diesel with a heat value of 42 Mj/Kg. It also increases efficiency by 25-30%.

A Zero Emission Technology Thermal Power Plant uses the CO2 in its flue gas, which is captured and recycled to produce a clean fuel called Dimethyl Ether (DME). DME is a clean fuel that can be used domestically instead of LPG or in transportation as a substitute for diesel or blended with diesel. It results in zero particulate emissions. This fuel can help solve the present uncertainty in the automobile sector by providing a stable alternative fuel without major changes in technology, and it serves as a technological intervention to achieve emission objectives until the next generation of automobiles takes over in the future. DME would result in near-zero CO2 emissions from diesel vehicles, while the power plant would also have zero emissions from its exhaust.

The present thermal power plants operating in India are subcritical plants, and their average efficiency has never exceeded 30%. Super Critical Power Plants in India operate at 40% energy efficiency. These supercritical power plants, using Oxy Fuel Combustion with CO2 sequestration, have an EEF of 45%. India has a total power generation capacity of 346.61 GW and is adding solar power on a large scale. This creates a grid stability problem, and hence, a total of 200 potential sites have been identified for setting up as many large thermal power plants with a total capacity of 428.9 GW, surpassing the existing installed capacity of 346.61 GW, according to a study by the Central Electricity Authority (CEA).

Clean Coal, Bright Future: Polygeneration Power

The push for solar power and wind power aims to increase the Solar wind Mix from 9% to 30%. However, this transition poses a challenge to grid stability. Therefore, the addition of cleaner coal technology is essential for ensuring power system stability and reducing CO2 emissions, especially considering that India is the third-largest emitter of greenhouse gases (GHGs) in the world.

The only long-term solution lies in adopting a polygeneration approach to power production. In this approach, coal/lignite is used to generate power, and the resulting CO2 emissions are utilized to produce a clean fuel called Dimethyl Ether (DME). This approach is imperative because global reserves of petroleum and natural gas are projected to be fully depleted in approximately 50 years. On the other hand, coal/lignite reserves can last for several centuries. Therefore, there will be a need for a cleaner alternative fuel, and DME serves as the silver bullet solution to resolve this paradox.

Fuel Chain Transformation: DME Production and Applications

The fuel chain that has been planned for the present project is first to convert the coal and carbon (from lignite) and carbon dioxide by a patented process of carbon recycling into DME and power in a polygeneration power plant. The process also utilizes methanol to seamlessly produce DME for various purposes:

1. Transportation: Converting diesel vehicles to use DME or DME blends for cleaner emissions.
2. Aviation: DME blends can be used as clean aviation turbine fuel or blended with aviation turbine fuel (ATF).
3. Domestic Fuel: DME can be used as a substitute for liquefied petroleum gas (LPG) or blended with LPG for domestic use.
4. Stationary Power Generation: DME can be utilized for applications such as standby stationary power generation.
5. Fuel Cells: DME can serve as a storage liquid fuel for fuel cell applications in hydrogen vehicles.

Clean and Efficient: DME-Diesel Blend for Automotive Applications

Dimethyl Ether (DME) is a colorless gas with a boiling point of -25°C. It is chemically stable and easily liquefied. DME requires about 75 pounds per square inch (psi) of pressure to be in liquid form. The interest in using DME as a fuel for diesel engines initially arose from a collaboration between Penn State and Air Products and Chemicals. They aimed to develop a campus shuttle bus that could run on DME. This project, supported by the Pennsylvania Department of Environmental Protection and the National Energy Technology Laboratory (agreement # DE-FG29-99FT40161), focused on blending DME with diesel fuel to ensure compatibility with existing diesel engine technology. Due to DME’s low viscosity (approximately 0.2 cSt at 40°C [1,2]), the blend ratio for the shuttle bus project is limited to 25 wt.% DME, a conclusion derived from another NETL-sponsored project.

The Government of India has recognized the DME-Diesel blend as an alternative fuel for compression-ignition engines in automotive applications to reduce pollution and emissions, resulting in soot-free exhaust. While DME is miscible in diesel fuel at any mixture fraction when held under pressures of 75 psi or above, the viscosity of the blends is below the ASTM diesel fuel standards. At 25 wt.% DME, the viscosity drops to approximately 1.39 cSt, which is the lower limit of the ASTM specification for diesel fuel viscosity. The DME blend serves as a cleaner substitute fuel for diesel vehicles, providing 25 to 35 percent better mileage and emitting less soot and carbon dioxide compared to similar diesel cars.

Diesel Emission Improvements through Oxygenated DME/Diesel Blend Fuels

Oxygenated DME has been proposed and tested as an additive to diesel fuel to reduce exhaust emissions. The addition of DME to diesel fuel leads to a decrease in the lower calorific value, aromatics fraction, and kinematic viscosity of the blended fuels. Simultaneously, the cetane number, C/H ratio, and oxygen content of the blends are enhanced, resulting in favorable effects on combustion and emissions when using blends with 10%, 20%, and 30% DME by mass. Performance and emission studies of diesel/DME blends are conducted in a direct injection (DI) engine, and the emission characteristics of four fuels are evaluated. At high loads, the blends significantly reduce smoke emissions with a minor impact on CO and HC emissions compared to diesel fuel. NOx and CO2 emissions are slightly decreased in the blends. At low loads, the blends have minimal effects on smoke reduction due to an overall leaner mixture. These results indicate the potential of diesel reformation for achieving clean combustion in diesel engines.

BRIEF BUSINESS AND FINANCING PLAN:

In addition to the technological aspects, a brief business and financing plan has been devised to support the implementation of this project. One key aspect of the plan involves converting the closed and stressed Gas Based Power Plants in India, which currently have no natural gas supplies, into Zero Emission Power Plants. These power plants would produce DME from their exhaust, utilizing non-peak power to produce hydrogen through the electrolysis of water. The CO2-rich flue gas from the power plants would serve as the feedstock for DME production, effectively converting CO2 into a high-value product. This process ensures that the main greenhouse gas, CO2, is not emitted but instead transformed into green DME fuel.

The basic equation to produce DME would be as follows:

2 CO₂ + 6 H₂ = CH₃OCH₃ + 3H₂O

The cost analysis reveals that the raw material cost for producing DME would amount to Rs. 2400/- for every 46 Kgs of DME, resulting in a cost of approximately Rs. 52.17 per KG. The emission intensity of Dimethyl Ether as Fuel is also impressively low, measuring ≤40 gms e/MJ, making it one of the cleanest fuels available. Furthermore, this process would result in the abatement of 88 Kgs of CO2 emissions.

For instance, in the case of converting a 1475 MW Gas Based Power Plant into a Zero Emission Power Plant, the plant’s Net Plant Heat Rate is determined to be 1750 Kcal/kWh. At full operational capacity, the plant would produce 35.4 million units per day. With a Calorific Value of 14500 Kcal/Kg for natural gas, the plant would require 4272.78 tons of natural gas per day, considering that one Kg of natural gas produces 8.285 units of power. Based on the current spot price of natural gas at Rs. 590/mmbtu or $7.62 per MMBTU, the average gas price would be approximately Rs. 3.34 per unit.

Through this conversion process, the Zero Emission Power Plant would abate approximately 19.824 million Kgs of CO2 per day, equivalent to 5.9472 million tons per annum over 300 operational days. The calculation is based on gas-based CO2 emissions of 0.56 Kg per unit of power produced.

To support the conversion of the power plants and the implementation of the DME production process, catalysts play a crucial role. Catalysts such as Cu.ZnO.Al₂O₃ on a silica base and γ-Alumina Catalyst are recommended for achieving a conversion rate of 35% per pass, while a three-reactor configuration is suggested to ensure complete reaction and better yields. The process optimization and fine-tuning would be based on field trials conducted under actual plant conditions.

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