Turning waste gases into power: saving money and the environment
4 min read
03 May 2017
4 min read
03 May 2017
Oil produced from offshore fields contains associated gases from oil drilling and boil-off gases from tankers and carriers, but these side streams with fluctuating compositions are usually treated as waste. However, Wärtsilä, with the help of a marine customer, decided to find a way to utilise these side/wasted streams as fuel gas in DF engine gas mode operation. The 1MW Pilot Wärtsilä GasReformer in Bermeo, Spain, was the result.
Gas reforming has long been a holy grail for the offshore sector. Oil produced from offshore fields contains associated gases, mainly consisting of natural gas (methane) and heavier gaseous hydrocarbons, such as ethane, propane or butane, with traces of even heavier hydrocarbons.
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’s methane number is too low, it will self-ignite. The engine knocks and needs to be derated to function properly. Derating implies reduced power output and decreased engine performance.
When gas varies in composition so that it cannot be utilised normally, such as in power generation, it usually is regarded as waste or cargo losses. So this gas is just flared, reliquefied or in the worst case, vented. Hydrocarbons are a far more harmful greenhouse gas than carbon dioxide due to their higher global warming potential. Not to mention it is also a waste of resources.
If there was a way of cleaning up this gas, it could be used. But although Wärtsilä knew that its offshore and marine clients would be very interested in a solution that meant they could use that waste gas, the company needed to prove it could be done.
The Wärtsilä GasReformer leaves Finland en route to Bermeo, Spain.
The challenge – turning waste gas into fuel
The idea for the project first bubbled to the surface in the autumn of 2015.
A Wärtsilä customer, one of the world’s largest marine energy transportation, storage and production companies, was very keen to look at gas reforming technology at work in the marine industry. It is a technology used mostly in the refinery and petrochemical industries, and Wärtsilä was determined to convince the customer that the technology could be transferred to a different environment.
The customer operates an offshore-to-shore shuttle service in the North Sea, which is an Emission Control Area (ECA), and there are limitations on the types of gas that can be vented – hydrocarbons and CO2 cannot be discharged, for example. On a five-day round trip of the shuttle service, the customer collected around 500 cubic metres of liquefied fuel (120,000 Nm3 VOC). The customer wanted to use it as fuel, instead of venting the gas into the atmosphere from the tank or just trying to push it back into the cargo.
The customer gave Wärtsilä the liquefied volatile organic compounds (LVOC), which is a very heavy hydrocarbon feed, to work with in the test unit with the Wärtsilä engine. That was the background for this test unit. (Figure 1)
The process – making heavy gases burn
The design engineering for the unit was completed in November 2015. From December 2015 to February 2016, the unit was built in Finland. It was then transported to Spain where Wärtsilä has engine test facilities. The unit completed the commissioning phase in the spring of 2016, and then there were some internal Wärtsilä tests in June.
The GasReformer’s technology is based on steam reforming (SR), a catalytic process familiar from the petrochemical industry and refineries, where traditionally hydrogen is produced from various hydrocarbon feeds. The Wärtsilä GasReformer exploits the same catalytic process but operates under different conditions. In the reformer, the methane number (MN) of any fuel gas is improved to 100 ± 5, by converting the heavier hydrocarbons to synthesis gas (H2 + CO) and finally to methane (CH4).
How does it work?
The Wärtsilä GasReformer takes the gas feed and ‘polishes’ it. It ensures that there is no sulphur left and then injects steam into the stream before feeding it into a catalytic reactor. On the catalyst surface, all the heavier hydrocarbons are split into smaller components, mainly methane and other constituents with only one carbon atom. The carbon chain is cut into small pieces and then built up again to finally form methane, with a little hydrogen and carbon dioxide produced, too. Then the Wärtsilä GasReformer cools it down, separates all excess steam in the system, and feeds it straight into the Wärtsilä 6L20DF engine. (Figure 2)
How did the Wärtsilä GasReformer perform?
In July 2016, a customer demonstration was carried out using the Pilot GasReformer in combination with a Wärtsilä 6L20DF engine. The GasReformer successfully demonstrated its capability to reform the LVOC into a high-quality gas that was successfully used in the Wärtsilä 20DF engine. Nitrogen oxide (NOx) emissions were also confirmed to follow International Maritime Organization (IMO) Tier III limits when operating the engine on reformed LVOC. Furthermore, successful mixing tests were completed on the engine using ratios of non-reformed LVOC mixed directly into LNG.
LVOC is a heavy-fuel gas, consisting mainly of C3-C5 components, which the engine could not take, even if derated. Therefore, if there is any interest in utilising VOCs or boil-off gases (BOG), e.g. from very large gas carriers (VLGC) or LPG carriers, as fuel for DF engines, there is no other feasible way than improving the MN (either by GR or mixing with LNG).
Despite working with extremely heavy fuel gas, the Wärtsilä GasReformer produced a final fuel gas that was running with lower NOx emissions than even natural gas.
By all measures, the demonstration for the customer was a success.
What are the reformer’s proven benefits to customers?
The Wärtsilä GasReformer in Bermeo, Spain, demonstrated its ability to reform LVOC into methane. It also makes it possible for the Wärtsilä GasReformer to utilise gaseous fuels that either contain large amounts of heavier hydrocarbons (C4+) or vary in their composition. Gases that were previously considered to be waste can now be converted into a valuable resource of energy.
Capital expenditure/operating expenditure (CAPEX/OPEX) concerns obviously still drive many customers, and this is where the Wärtsilä GasReformer excels.
By reducing greenhouse gases (GHG) emissions from the oil and gases value chain, through recovering vented and wasted hydrocarbons and utilising them for power generation, the operator or owner will get remarkable savings. For example, in fuelling costs, bunkering and transportation, saving could be around 50%.
When it comes to LNG-powered vessels, the GasReformer technology can be utilized for fuel gas quality control taking care that the methane number of the fuel gas to the DF engine is always above 80. This methane number control onboard will allow flexibility in LNG quality and bunkering. (Fig 3).
Fig. 3 - Fuel gas quality control with a GasReformer allows flexibility in LNG quality and bunkering on LNG-powered vessels.
The environment also benefits
This new process boasts the environmental benefits derived from converting waste gas into usable fuel. Offshore gas flaring is increasingly recognised as a major environmental problem, causing 400 million tonnes of CO2 in annual emissions, not to mention the valuable resources that go to waste. When considering the vented BOGs, i.e. the VOCs from the marine industry, the overall GHG effect becomes even more pronounced.
With the Wärtsilä GasReformer, this waste gas can be reliably and efficiently used by Wärtsilä dual-fuel (DF) engines. When utilising associated gas or recovered BOGs from tankers or gas carriers as a reliable source of energy, the operator can achieve self-sufficiency in terms of energy supply. Thus, the need for fuel bunkering or BOG reliquefaction, both costly operations, decreases. With a Wärtsilä 10 MW GasReformer combined with a DF engine, the operator can reduce the need for bunkered fuel oil by 39 tonnes per day (TPD) and reduce flaring by more than 1.1 million standard cubic feet of gas per day (MMSCFD), which equals >100 TPD equivalent carbon dioxide (CO2eq). Where VOCs are usually vented, GHG emissions are reduced by 10.6 TPD CO2eq per ton of recovered VOC.
Which industry will benefit most from the Wärtsilä GasReformer?
The offshore industry stands to gain the most because the biggest benefit to the offshore industry is the immediate reduction in the costs for primary fuel, transportation and bunkering. The offshore industry with all oil and gas production units does also have best knowledge and understanding on gas treatment processes.
If a customer is producing, for instance, LNG offshore, there are side streams such as natural gas liquids from LNG production or boil-off gases. These and other side streams can be utilised for power generation, so there will be no need for handling equipment of side streams such as reliquefaction, storage or shipping.
Also LNG-powered vessels in the marine industry can benefit from this technology, if it can guarantee full-load operation of the engine without limitations in LNG quality or bunkering. This fuel gas quality control will ease the operation and improve flexibility.
The investment into new, green technology, will usually have a payback time of one to three years.
Wärtsilä proved that the GasReformer can make use of gaseous fuels that either vary in their composition or contain large amounts of heavier hydrocarbons. Gases that were previously considered as waste can now be converted into a valuable energy resource. Especially in the offshore and marine industries, where cost savings and compliance with environmental regulations are critical, this development is significant.