GAS REFORMING CREATES master

Gas reforming creates fuel from waste

Oil produced from offshore fields always contains associated gas, mainly consisting of natural gas (methane) and heavier gaseous hydrocarbons, such as ethane, propane or butane. This gas often varies in composition and can thus not normally be utilized e.g. in power generation - instead it is usually regarded as waste.

Text: HARRIET ÖSTER Photo: -

Oil produced from offshore fields always contains associated gas, mainly consisting of natural gas (methane) and heavier gaseous hydrocarbons, such as ethane, propane or butane. This gas often varies in composition and can thus not normally be utilized e.g. in power generation - instead it is usually regarded as waste.

Heavier hydrocarbons have low fuel quality, indicated by a low methane number – the measure of ability to withstand compression in the engine before ignition. If a gas’ methane number is too low, it will self-ignite. The engine knocks and needs to be de-rated to function properly. De-rating implies reduced power output and decreased engine performance.

Thus heavier gaseous hydrocarbons are usually just flared or, in the worst case, vented. Hydrocarbons are a far more harmful greenhouse gas than carbon dioxide due to their higher global warming potential.

UTILIZATION INSTEAD OF FLARING

“In oil production, associated gases have been regarded as a problem, since solutions other than flaring have been difficult, unreliable and expensive. These gases could be used as fuel in some boilers, but that is expensive and has a low efficiency. Gas turbines, meanwhile, are very sensitive to variations in the composition and quality of gases,” says Product Manager Peik Jansson, Flow and Gas Solutions, Gas Recovery at Wärtsilä Ship Power.

The new Wärtsilä GasReformer provides an alternative to flaring. In a process based on steam reforming, the non-methane hydrocarbons are catalytically converted into methane. Regardless of the initial quality of the gas, a methane number close to 100 – describing pure methane – is achieved. For combustion gas engines to work properly, the methane number of the fuel must be above 80.

“Even a very small amount of heavier hydrocarbons in the gas pushes down the methane number drastically,” Jansson points out.

The amounts of gas flared in the oil industry are huge. The World Bank-led Global Gas 
Flaring Reduction Partnership estimates that around 150 billion cubic metres of gas are flared or vented in the world every year. Flaring causes some 400 million tonnes of carbon dioxide in annual emissions. The Partnership works to reduce flaring globally, and it has indeed been banned in several countries. The flaring of offshore gas alone is estimated to produce more than one percent of global CO2 emissions.

FIRST CUSTOMER: A CHINESE OIL PLATFORM

Wärtsilä GasReformer technology is based on steam reforming of gaseous hydrocarbons, where the hydrocarbons react with steam in the presence of a catalyst. Steam reforming is a well-known conversion process, frequently used in the petrochemical industry. Wärtsilä has been developing the process and adapting it for use in the GasReformer over the past 5–6 years.

The prototype using Wärtsilä-developed technology was thoroughly tested at Vaasa Test Laboratory in Finland. The decision to industrialize the technology as a customer offering was made in 2010, after which design work started. By 2012 the GasReformer had been designed, build, tested, sold, and delivered to the first customer, a Chinese oil platform under construction.

“The project task was to develop the technology for use under offshore conditions, with all the subsequent requirements. That implied thorough validation and security tests for new technology and approval by a classification society. For Wärtsilä this was a leap; we have lots of experience in assessing power technology, but not process technology,” Jansson says.

GAS REFORMING CREATES 2

Wärtsilä owns the patent for the GasReformer application of steam reforming. The reactors, the lay-out, and the process control are Wärtsilä’s own design, while the catalyst used in the reactions is bought on the market, along with many of the other components.

FLOATING STORAGE TANKS SELF-SUFFICIENT IN POWER

Design of the GasReformer was under way and building of the pilot was about to start when Wärtsilä acquired the engineering company Hamworthy at the beginning of 2012. Hamworthy’s broad knowledge of processes in the offshore oil & gas industry has been of great importance when developing customer applications for the GasReformer. Testing of the
GasReformer started in the end of 2012.

“We have close co-operation and have found several new ways to utilize the GasReformer that we had not thought of,” Jansson says.

“Our colleagues at Wärtsilä-Hamworthy  helped us realize that you get the greatest advantage from the technology by recovering gases that evaporate from the crude oil in the large, floating storage tanks at offshore oil production sites.”

In crude oil pumping and handling, the crude is heated to improve its viscosity. When heated, hydrocarbon fractions of the crude evaporate in the storage tank. These volatile organic compounds (VOCs) are traditionally vented into the atmosphere together with the nitrogen gas used as a security shield on top of the crude.

“These volatile hydrocarbons can be recovered, and then converted to fuel with the 
Wärtsilä GasReformer, to be used by a Wärtsilä dual-fuel engine for producing power. Thus the storage and offloading vessel becomes self-sufficient in the power needed for pumping crude oil from the storage to transport vessels,” Jansson says.

“Loading crude is a fast operation and the pumps need a lot of power. When you are able to utilize VOCs as fuel for power generation, the customer gets a financial benefit. At the same time the amount of greenhouse gases emitted into the atmosphere is reduced. The need for bunkered marine diesel oil for the engines decreases significantly, and you save in diesel oil transport costs as well.”

“Finally, the Wärtsilä GasReformer is not only a solution for utilizing VOCs or associated gas. It also improves the performance of Wärtsilä dual-fuel engines. Together they constitute a system that produces electricity with an overall efficiency of up to 44 per cent,” Jansson points out.

Reforming in honed chemical reactions

THE PATENTED WÄRTSILÄ GasReformer shows the company’s expertise in reforming gaseous fuels, and has its origin in the development work done on fuel for fuel cells. Fuel cells run on very pure methane so a pre-reformer is required to boost fuel purity. From there came the idea: why not try this on engine fuel too?

THE STEAM REFORMING process used in the Wärtsilä GasReformer is an adaptation of the conversion process frequently used in the petrochemical industry to produce synthesis gas from natural gas.

“STEAM REFORMING IS normally used to produce syngas – that is, hydrogen together with carbon monoxide – from methane reacting with steam. The Wärtsilä GasReformer works under other conditions, because we want to produce methane from the process. The GasReformer first converts heavier hydrocarbons to synthesis gas, from which methane is then derived,” explains GasReformer Expert Reetta Kaila, Flow and Gas Solutions at Wärtsilä Ship Power.

THE PROCESS INCLUDES two reactions taking place simultaneously on a catalyst bed. In the first reaction, hydrocarbons react with an excess of steam to form syngas. In the second, the components of the synthesis gas react to form methane. In effect, the balance of the traditional steam reforming process is driven backwards.

“THE FIRST REACTION needs heat, while the second one produces it. In this way the reactions support each other in the energy balance,” Kaila says.

THE NICKEL CATALYST used in the process is highly sensitive to sulphuric compounds. Gaseous hydrogen sulphide may be present in associated gas, so desulfurization vessels have been included in the system, upstream of the reformer.

“THERE HAS BEEN CERTAIN CHALLENGES in the process, but nothing that cannot be overcome,” Kaila believes.

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