Ricardo is designing, installing and operating a combined heat and power demonstrator plant with a carbon negative footprint to showcase climate repairing technology, and demonstrate the effectiveness of community scale negative emission technology plus clean energy using sustainably-sourced forestry waste.
Ricardo is leading the consortium delivering the demonstrator plant. The consortium combines an innovative carbon capture system developed by Ricardo with the hot air turbine technology from Bluebox Energy and pyrolysis technology from Woodtek Engineering.
The technology processes the forestry waste in three ways: producing biochar; generating heat and power; and capturing carbon dioxide from the exhaust. It also produces commercially marketable carbon products: the biochar can be used by farmers to enrich soil and add to animal feed to reduce ruminant emissions. The food-grade carbon dioxide can either be used for making low-carbon concrete or in the food and drinks industry to replace carbon dioxide derived from industrial processes which rely on imported natural gas.
But what is biochar? How does it help to store carbon, and just how can we capture carbon dioxide? Here, Jonathon McGuire from Bluebox Energy tells us more.
What is biochar?
JMcG: “Biochar is a charcoal-like substance but is highly porous, lightweight, fine-grained and has a large surface area. It is usually made by burning wood. Although it looks a lot like common charcoal, and is usually made by burning wood, in fact biochar is actually produced using a specific, controlled process called pyrolysis. During pyrolysis organic materials, such as wood chips, leaf litter or dead plants, are burned with very little oxygen. This converts them into biochar: a stable form of carbon that can’t easily escape into the atmosphere. Biochar is far more efficient at converting carbon into a stable form and is cleaner than other forms of charcoal.”
How does biochar capture carbon?
JMcG: “As a tree grows, it captures carbon dioxide from the atmosphere and fixes it into organic material in the trunk, branches and leaves. In softwood timber forests, the trees are harvested when their initial vigorous growth slows, usually after 40 years. During tree felling and logging, about 20% of the tree is left behind. During the sawmill process a further 30% of the tree is lost. Therefore, 50% of the tree volume is ‘wasted’. This waste wood can be used for the biochar process. Of the whole tree’s carbon store, half is converted into timber, a quarter can be turned into stable biochar leaving a quarter converted into hydrocarbons.”
How do we capture carbon dioxide?
JMcG: “During the pyrolysis process, the hydrocarbons are burned in a combustor to produce heat. This heat is first used to generate electricity and then used to generate steam. Our process also includes a CO2 absorption cycle. In this cycle, the flue gas is passed through an absorber column containing a solution at about 40 degrees Celsius. In this column, the solution absorbs the carbon dioxide leaving the exhaust to be a mixture of Nitrogen and Oxygen (effectively air with a lower percentage of oxygen). The solution is then pumped into a stripper column where it is heated using steam to liberate the carbon dioxide. This carbon dioxide is extremely pure at ~99.9%. The solution is then cooled before being recycled into the absorber column.”
How does a hot air turbine work?
JMcG: “A hot air turbine takes in filtered air and compresses it in a turbocompressor. This air is heated using energy from a hot gas stream, in this case the flue gas from the pyrolysis combustor. This hot pressurised air passes through the turbocompressor and power turbine to produce electricity. The electrical output from the turbine generator is converted to high quality grid power in a dedicated inverter. The air that comes out of the power turbine is still about 400 degrees Celsius, so can be used for heating, steam production or direct drying.”
Where are hot air turbines are used?
JMcG: “Bluebox Energy has a number of installations including:
Biomass waste wood combustion in Switzerland
Concentrated solar power in Almeria, Spain
Biochar production in Fehraltorf, Switzerland
Waste heat recovery in Gwangju, South Korea”
Why use a hot air turbine for this negative emission cogeneration technology?
JMcG: “Our negative carbon emission technology needs steam at 145 degrees Celsius to drive the carbon dioxide capture process. Of the technologies available, only hot air turbines discharge air at a high enough temperature (~400 degrees Celsius) to generate steam. In addition, hot air turbines have a number of advantages over other heat to energy technologies: they are made of proven components with millions of operating hours in the stationary power and marine industry; there is no need for a condenser, with much reduced ancillary power requirements; and non-hazardous fluid (air) is used (no toluene, pentane, thermal oil or R245fa). Also, they are easy and fast stop-start with no impact on equipment.”
How can the technology be net energy positive?
JMcG: “A full scale plant consumes 2800 kg/h of waste wood, producing 280kg/h of biochar, 3.5MW of heat and 320kW of electricity. The plant requires 2.2MW of heat to dry the incoming waste wood and drive the carbon dioxide capture process leaving 1.3MW for local heating requirements. The plant also requires 160kW of electricity to run the pumps and fans, but this still leaves 160kW to be used by the customer or can be exported to the grid.”
Where is the negative emission cogeneration technology going to be used?
JMcG: “Our negative emission cogeneration technology is an attractive solution for businesses who already operate combined heat and power (CHP) systems and have a need for one or both the biochar and the carbon dioxide. Examples of such businesses include food and drinks manufacturers, commercial greenhouses, anaerobic digestors, concrete manufacturers and waste-water treatment sites.”
When will the technology be ready?
JMcG: “The demonstrator plant will be installed and operational by the end of this year. This will generate the data needed to validate the design and other factors such as the operating costs. We can deliver technical feasibility studies in 2023, using the currently available designs, and offer a full-scale roll-out of the technology from 2024.”
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