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Putting carbon dioxide to work

The growth of greenhouse gas emissions and concerns about climate change are increasing worldwide interest in the capture, disposal, and utilisation of CO2 from power plants and industrial processes. AGA recently commissioned a major new plant at Neste Oil’s refinery at Porvoo that sets a new standard in on-site CO2 recovery.

Energy utilities have been among those most in the public eye in recent years when it comes to reducing industry’s carbon footprint and helping mitigate the onward march of climate change.

For utilities with coal-fired generating capacity, there are three main alternatives for capturing the CO2 their plants release: precombustion, post-combustion, and oxyfuel.

In the case of precombustion, carbon is removed from the fuel prior to combustion, and in the case of post-combustion from flue gas before release to the atmosphere. The most commercially attractive option, however, appears to be oxyfuel, and there are a number of projects under way in Europe, Finland included, to further develop and test this technology.

The technique involves burning coal in pure oxygen instead of air. This results in a nitrogen-free flue gas rich in CO2 that can be purified, compressed, and stored for onward transport by ship or pipeline. Should disposal be the preferred route, the disposal options available today for handling large quantities of captured CO2 are minimal; using depleted oil and gas wells or mines appears the most promising.

Combined industrial recovery

AGA’s new CO2 recovery plant at Porvoo combines two separation methods in a large-scale facility that is one of Europe’s biggest.

Other areas of industry also generate large amounts of carbon dioxide, and industrial gas companies have been working on a number of techniques for recovering this gas for many years. The signing of the Kyoto Protocol and the start of emission trading have only highlighted the importance of this work and the need to push it further ahead.

Ironically, the success that has been achieved in reducing the CO2 content of the gas flows in industrial processes is presenting its own challenges in recovering the remaining carbon dioxide.

AGA’s new recovery plant at Neste Oil’s refinery at Porvoo in Finland, commissioned at the end of 2006, addresses this problem by combining two separation methods in a large-scale facility. With a capacity of 400,000 tonnes a year, its is some 10 times larger than a conventional unit, and is one of Europe’s largest.

In the first phase, the carbon dioxide content of the raw gas is first increased by means of a PSA or Pressure Swing Absorption process, after which the CO2-rich end-product is liquefied and purified.

The AGA plant takes its feedstock from the steam reformer that lies at the heart of a hydrogen plant built by Neste Oil to supply an advanced new 1 million t/a line commissioned this year. The latter produces premium-quality, sulphur-free diesel fuel from low-value fuel oil. Hydrogen from the plant, which is ‘fired’ on natural gas and steam, is also used at Neste Oil’s new biodiesel plant to break down the large fat molecules contained in its vegetable oil and animal fat feedstock.

Carbon dioxide from the new plant will be mainly delivered by sea to AGA customers in the Baltic countries, Russia, Sweden, and Norway. Customers in Finland will be supplied by road. The new plant brings a major boost to carbon dioxide production at the Porvoo site, where AGA has had a small CO2 plant in operation since 1993.

The Coral Carbonic has been specially built to carry CO2, stored under pressure at –20 – 30°C, from the new plant at Porvoo to customers around the Baltic.

Supplying regional markets

The Porvoo plant helps Neste Oil cut its carbon dioxide emissions and further reduce its overall carbon footprint – cost-effectively – and gives AGA and its parent company, Linde Gas, one of the world’s leading supplier of carbon dioxide applications, a cost-effective, high-volume solution for meeting its growing supply needs.

Demand for CO2 is on the increase, as it is becoming more popular in food manufacturing and brewing and in the paper and pulp industry, as a chilling medium during transport, and in industrial welding applications. In fact, the gas has been in short supply in a number of countries in Central Europe recently.

Carbon dioxide is also used being in increasing volumes in various environmental applications, as it can replace many chemicals, such as acids, that are more detrimental to the environment.

Carbon dioxide recovery at Porvoo helps Neste Oil reduce its carbon footprint and gives AGA a cost-effective, high-volume source of quality gas.
> Jukka Gustafsson
(Published in HighTech Finland 2008)