Reduction of CO2 emissions from the combustion of gaseous fuels in boilers

M.A. Savitenko , Director of Autonomous Non-commercial Organization “Center for Research and Scientific Development in the field of energy “Hydrogen Technology Solutions”

B.A. Rybakov, Chief Technologist of Autonomous Non-commercial Organization “Center for Research and Scientific Development in the field of energy “Hydrogen Technology Solutions”

One of the ways to reduce the specific CO2 emissions of boilers is to increase the efficiency of the boiler by condensing the water vapor of the flue gases.

When burning natural gas, the use of the heat of condensation of water vapors of flue gases, the efficiency of the boiler unit can be increased by 10-11%.

The resulting condensate will be saturated with carbon dioxide.

To use the condensate, the carbon dioxide must be removed using a decarbonizer.

One way to neutralize the carbon dioxide dissolved in the condensate is to add caustic soda.

When burning natural gas, the following components will be present in the flue gas composition:

1. Nitrogen
2. Oxygen
3. Carbon dioxide
4. Water vapor
5. Nitrogen oxides

When water vapor condenses, additional thermal energy can be obtained. If additional heat is not required, then you can reduce the consumption of natural gas. If the consumption of natural gas is reduced, the carbon dioxide emissions into the atmosphere will decrease proportionally.

The second way to reduce carbon dioxide emissions is to switch to burning hydrogen. The combustion of hydrogen does not produce carbon dioxide.

When burning hydrogen, the following components will be released into the atmosphere:

1. Nitrogen
2. Oxygen
3. Water vapor
4. Nitrogen oxides

The highest heat of combustion of hydrogen is 140 MJ/kg, and the lowest is 120 MJ/kg, therefore, the use of codensation boilers for burning hydrogen will allow you to get 18% more thermal energy than when burning natural gas.

Since the resulting condensate will not contain carbon dioxide, it can be used both to feed the boiler, and as water to produce the electrolyte, which is necessary for the production of hydrogen in the electrolyzer.

The resulting condensate can also be used to produce steam, which is needed to produce hydrogen from natural gas by steam conversion.

A third option to reduce carbon dioxide emissions is to burn a mixture of natural gas and hydrogen, or hydrogen-containing gas, in a boiler.

To provide heat to remote consumers, you can consider the following options:

• Propane/butane fired boilers;
• Natural gas fired boilers;
• Boilers running on hydrogen;
• Boilers that run on a mixture of natural gas and hydrogen.

At the same time, it is necessary to ensure the supply of fuel over long distances.

Table 1 shows the values of the lowest heat of combustion of various substances:

Specific heat of combustion of substances, MJ / kg

From this table, it can be seen that the highest value of the mass heat of combustion is hydrogen.

It was noted above that when burning hydrogen in a condensing boiler, 140 MJ of thermal energy can be obtained from each kilogram of hydrogen.

Hydrogen can be produced from the water in the cell using wind or solar electricity.

As water for the production of hydrogen, you can use condensate obtained in a condensation boiler.

This technical solution allows you to provide remote consumers with “green” electricity and “green” heat.

If we compare the mass consumption of hydrogen burned in a condensing boiler with the mass consumption of other fuels burned in conventional boilers with the same amount of heat generated, we get the following relations:

• Mass consumption of natural gas / mass consumption of hydrogen – 2.92.
• Propane mass flow rate / hydrogen mass flow rate-2.95.
• Mass consumption of diesel fuel / mass consumption of hydrogen – 3.29.
• Mass consumption of fuel oil / mass consumption of hydrogen – 3.57.

Therefore, the specific cost of delivering hydrogen should be lower than the cost of delivering other energy carriers.

It should be noted that with a decrease in the mass heat of combustion of combustible substances, carbon dioxide emissions into the atmosphere increase, since the chemical composition of these substances increases the mass ratio of carbon to hydrogen-C / H, and the mass heat of combustion of carbon is 34.1 MJ/kg, which is significantly lower than the mass heat of combustion of hydrogen.