Horticulture sector replaces fossil fuels with sustainable energy sources

Demand for a reliable CO2-source
Food & Pharma
7 January 2019

The energy transition - replacing fossil fuels with sustainable energy sources - is proving a challenge in all sectors, but the situation in the horticulture sector is especially complex. This is because protected crops actually need carbon dioxide to survive.

Plant growth is based on the photosynthesis principle, where carbon dioxide (CO2) and water are absorbed and, under the influence of light, transformed into sugars, starch and cellulose. “If a plant is lacking either one of these, it has a negative effect on production and plant quality,” explains Arlo Saes, Business Developer Food & Agro at Air Liquide.

Adding pure CO2

“Between April and September, the light on sunny days can be intense, and plants will quickly consume all the CO2 in the greenhouse. As the CO2 level drops, crop growth is hampered.”

To meet this challenge, Air Liquide has developed a CO2 dosing system to inject pure CO2 as required, based on measurements by greenhouse sensors connected to a computer. When the level sinks below the desired ppm value, the system injects CO2 until the level is again optimal.

Heating in summer?

Horticulture companies can also generate CO2 through the combustion of flue gases in a boiler or cogeneration installation (CHP). Combustion of natural gas produces flue gas CO2, which can be deployed in the greenhouse. “However, flue gas CO2 dosing does come with a few disadvantages. For example, the combustion of natural gas in the summer creates too much heat. And of course it’s not sustainable to burn gas when the heat isn’t even needed. In these circumstances, adding liquid CO2 is the ideal solution to keep greenhouse CO2 levels up sustainably.”

“Of course liquid CO2 can be added in the winter as well. With young plants and mostly closed air vents, greenhouse air change rates can be very low. This risks harmful and toxic substances accumulating - such as ethylene, sulphur dioxide, nitric oxides, acetylene or propylene - released by the CO2 recovered from a boiler or CHP. This hazard will continue to grow as protected cropping moves increasingly towards closed greenhouses.”

Sustainable energy

The Dutch horticulture sector has joined with government to draw up goals in the ‘Clean, efficient agricultural sectors’ agreement. In the agreement, the protected cropping sector commits to transitioning in the near future from fossil fuels to sustainable energy sources such as geothermal heating systems and heat networks. The intention is to move to at least 20% sustainable energy by 2020 and even 100% by 2050. As a result of this energy transition, the availability of flue gas CO2 is in decline, making horticultural companies more dependent on CO2 from other sources.

“It’s clear that the demand for CO2 for protected crop production will rise steeply. This is one reason why Air Liquide is constantly investing in new, sustainable sources of CO2. For example, AVR and Air Liquide recently signed an agreement for CO2 capture. This will improve the availability and reliability of liquid CO2 supply.”

The CO2 is delivered by tanker, chilled and pressurised, and then pumped into the customer’s storage tank. Air Liquide storage tanks have been specially designed to store liquids under pressure and meet strict Pressure Equipment Directive requirements. From the tank - the capacity of which depends on greenhouse size and ranges from 6,000 to 60,000 litres - the liquid CO2 is piped to the gardener’s CO2 unit, where it is subsequently vaporised for distribution throughout the greenhouse.

Costs and benefits

“Customer investment in a liquid CO2 installation is low, since Air Liquide assumes full responsibility for the costliest part - the storage tank. One of our experts visits the site to determine the cost of the required materials for the liquid CO2 dosing and vaporisation.”

Air Liquide isn’t just the European leader in CO2 production, it also maintains the most CO2 plants in Europe, guaranteeing reliability of supply.

For further information contact Mr Arlo Saes at arlo.saes@airliquide.com or call +31 20 795 66 21.

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