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The problem

Combustion processes in power plants, waste-to-energy plants, biomass-to-energy plants etc. release enormous quantities of CO2 in the atmosphere. CO2 is the main greenhouse gas, at the root of the dramatic climate change the world is experiencing.

The combustible matter in any fuel, fossil or non-fossil (biomass, waste, RDF,...) consists mainly of hydrocarbon molecules (CxHy). Non-combustible matter can also be present, as inert matter (minerals, sand) and/or water.

In a power plant the energy in the fuel is released by combustion, a process that takes place in the furnace or combustion chamber. Combustion is oxidation, i.e. reaction with oxygen. Carbon becomes carbon dioxide and hydrogen becomes water (vapor).

The oxygen is supplied by using outside air, which contains (only) 21% oxygen (by volume). The rest is mostly nitrogen (N2) and less than 1% other gases (water vapor, CO2, noble gases).

Standard Plant

The main components of a standard solid-fuel fired power plant are:

  • The furnace, where the solid fuel is converted to hot flue gas, using combustion air.

  • The steam boiler, a huge heat exchanger: the flue gas transfers its heat to make steam

  • The steam cycle plant that uses the steam to drive a turbine and/or for heating applications

  • The flue gas cleaning system, to treat the flue gas and meet the emission requirements

For a better way: SEMS-OFC

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In the furnace the solid fuel hydrocarbon molecules react with the oxygen from the combustion air. Carbon atoms become carbon dioxide (CO2), hydrogen atoms become water vapor.

Many other reactions take place between the various atoms in the fuel and the air.
Almost all of the energy is produced by the two basic reactions.

Although the 'rest' fraction in the flue gas is less than 1% of the total, it is cause of the pollution and thus this fraction requires all the attention in the flue gas cleaning.

This video shows the conversion of solid fuel fractions and combustion air into flue gas fractions.

The solution: SEMS-OFC

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SEMS-OFC is patented!

The basic SEMS-OFC© plant uses the same components as a standard plant, with the following fundamental changes:

  1. instead of combustion air, an artificial combustion gas is used with the same or a similar oxygen concentration. This 'oxy-gas' is a mixture of pure oxygen and recirculated flue gas, mainly consisting of CO2.

  2. the flue gas cleaning system contains a condensation step, i.e. the moisture is removed from the flue gas by cooling the flue gas to below saturation temperature.

  3. The remaining clean flue gas is now more than 90% CO2 and is readily available for storage or utilization.

The next step: SEMS-OFC+

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Advantages of SEMS-OFC

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  1. No need for new components

  2. Can be retrofitted on existing plants

  3. Water recovery from the flue gas

  4. Extra heat recovery from the flue gas

  5. Oxygen concentration of the 'oxy-gas' can be tuned to the fuel for higher efficiency

  6. The plant has an overall higher thermal efficiency (compared to standard plants using air)

  7. All CO2 is readily available for storage or utilization (current CCU/S plants recover only a fraction)

  8. No need for a separate, expensive and inefficient Carbon Capture system

  9. Can be extended to own O2 production, with green H2 as byproduct

  10. Can be extended to production of chemicals (e.g. methanol)

Oxygen

If you want to use industrial oxygen in large quanties, you can:

  • buy it on the market

  • make it yourself, using one of the
    existing methods

Ways to make industrial oxygen:

  • Cryogenic (fractional distillation of liquefied air), the most common method

  • Non-cryogenic methods

    • VPSA (vacuum pressure swing absorption)​

    • electrolysis

Background info:

  • The world industrial oxygen market is 380 million tons per year (2018)

  • The main users are:

    • steel industry : 55%​

    • chemical industry: 25%

    •  remainder (medical, welding, rocket propellant oxidizer...): 20%​

SEMS-OFC+

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A next development is the own production of oxygen.

This can be:

  1. a cryogenic plant

  2. electrolysis, i.e. using electricity to split water in hydrogen and oxygen

 

Both methods use the power produced by the plant.
In addition, electrolysis can also use the recovered water (it needs to be demineral-ized).​

Electrolysis consumes a lot of power, much more than the WtE plant can produce. 

On the other hand, it produces very valuable fuel: green hydrogen!

The next step: SEMS-OFC+X

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SEMS-OFC+X

The schematic diagram shows a SEMS-OFC© process, with own production of O2 and H2 (as before) plus addition of a methanol synthesis plant (existing technology!) that converts the CO2 and H2 into methanol, a base product of the chemical industry

('Direct CCS/U').

Similar other solutions can be developed to convert the CO2 to 'X' (chemicals).

CH OH

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