Fig. 1 – The Wärtsilä solution for re-injecting associated gas into the oil well. This maintains the pressure, enhances oil production, and can even be used as a means of storing gas for later use.

[ IN DETAIL ENERGY ]

Gas-diesel conversions
for power plant applications

AUTHORS:

JYRKI ANTURANIEMI, PROJECT PROPOSAL MANAGER, PROJECT PROPOSALS, SOLUTION MANAGEMENT | SERGEY CHEPRASOV, PROJECT MANAGER, SERVICES PROJECTS NORTH AMERICA | HEIKKI HUHTALA, PROJECT MANAGER, SERVICES PROJECT CENTRE FINLAND

Wärtsilä´s gas-diesel (GD) technology was introduced in 1987 with the Wärtsilä 32GD, the first gas engine in the Wärtsilä portfolio. This technology has been used mainly in offshore applications, but has later found applications in the power plant sector.

GD technology makes it possible to run a power plant on either associated gas or crude oil, where the gases could contain heavy hydro-carbons, or heavy fuel oil to provide the operator with fuel versatility and security against gas supply disturbances. The system accommodates daily/frequent variations in gas quality and quantity.

GD- power plants

In power installations, the economic viability of gas is becoming ever more apparent. At the same time, emission issues related to the use of liquid fuels are becoming more complex. Not surprisingly, therefore, the use of gas to generate power is rapidly increasing, although in order to convert older LFO /HFO operated installations to natural gas, there needs to be a reliable supply of gas available. Nevertheless, the conversion of a HFO plant to natural gas offers several benefits that make this upgrading feasible for many customers. Currently, a conversion project can be offered using most of the Wärtsilä 32, Vasa 32 and Vasa 46 engines. Typically, the two main drivers for fuel change are:

  • Reduced emissions and fees
  • Reduction of fuel costs.

The GD conversion concept

Wärtsilä's gas engine portfolio (GD, SG and DF types) is well known, and if the current total running hours are, for example, less than 10,000 hours, a GD conversion is feasible. In any case, the number of engine parts that need to be changed is limited. Diesel engines provide one of the best heat rates, while GD engines in addition to this also enable the use of most gas types available on the market.

There are a number of factors to take into account when considering a gas conversion. The most logical place to start is to establish whether or not the existing engines on site can be converted, or if they should be exchanged for new ones. Converting an existing engine is usually economically more feasible than installing a new one, especially since a conversion basically brings the same benefits as a new engine. For example, the same warranty is granted as for a brand new engine. Furthermore, there are also savings to be made on maintenance costs since the running hours are reset to zero (0). However, with smaller installations, e.g. below 10 MW, it would most likely be more cost effective to install new engines. The plant equipment required for operating on gas can be divided into six main areas:

  • Gas delivery
  • Gas compressor
  • High pressure gas
  • High gas pressure oil
  • Control
  • Electrical feed.

Each gas conversion is installation specific, and requires a basic engineering evaluation before a detailed offer and scope can be given. The scope can encompass a turnkey delivery that includes the installation and commissioning of the plant. The plant’s gas supply and gas line connection to the gas delivery system is normally the responsibility of the customer. The most important benefits of such a conversion are lower emissions, improved plant efficiency, and the fact that all the work can be done on site.

Currently there is an upsurge in demand for gas conversion installations, based on an increase in gas supply. In countries without pipeline gas, liquefied natural gas (LNG) offers a potential alternative solution.

Gas conversions are yet another example of Wärtsilä´s ability to help owners and operators throughout the lifecycle of their investment, and the company can offer a broad variety of possibilities to meet each customer´s specific requirements.  Wärtsilä is also supporting its customers in gas conversions by providing relevant training courses on gas operation

Eden Yuturi Conversion Project

In 2008, PETROAMAZONAS EP (PAM), an Ecuadorian state owned oil company, initiated a mission named “Optimisation Generation Electric- OGE” that they also nominated as a Waste to Wire, or Well to Wire (W2W) project.

During the crude oil extraction process, crude oil, water, and associated gas come to the surface, where they are then separated at the production facilities (see Figure 3).  Given the unstable condition of the associated gas (both in terms of composition and supply) it is usually vented or flared. The World Bank-led ‘Global Gas Flaring Reduction Partnership’ estimates that globally this amounts to approximately 150 billion cubic meters of gas each year, causing some 400 million tons of carbon dioxide emissions. That is equivalent to 30 per cent of the European Union’s total gas consumption. It is important to point out that associated gas is quite different to natural gas, in that its composition and volumes change significantly over time.  If you add to this the fact that the supply of associated gas is extremely unstable (see Figure 3), it becomes clear why in most cases the oil companies prefer to simply vent or flare it.  

In order to reduce gas flaring at the Eden Yuturi site, PETROAMAZONAS EP and Wärtsilä entered into a joint development agreement aimed at developing an integrated "gas/crude" product, able to cope with the dynamic condition of associated gas. In line with the technological developments, PAM and Wärtsilä jointly developed the Clean Development Mechanism (CDM) programme as a means to co-finance the project. The objectives of the project are to mitigate the environmental impact through reducing the exhaust and noise emissions; to develop and implement a flexible solution that will adjust to the challenging conditions of associated gas; and to replace the use of diesel/crude oil for power generation by utilizing the associated gas.

Technology

Thanks to Wärtsilä's multi-fuel technology, associated gas can be converted to electricity instead of being continuously flared into the atmosphere. This technology offers a unique degree of fuel flexibility, permitting the engines to run on any combination of liquid fuel and associated gas. This is essential for oil and gas companies operating in environments where the associated gas volumes and composition are constantly changing. This flexibility in the utilization of associated gas serves to maximize power production while, at the same time, reducing greenhouse gas emissions.

Although the first phase of the project has been completed, PAM and Wärtsilä are already looking at taking the "energy efficiency" concept to a next phase by developing new state-of-the-art technological features. The overall goal is to eliminate any waste, thereby allowing PAM to reduce the "carbon footprint" per barrel of crude oil extracted. 

The Project Outcome

The conversion of the Eden Yuturi power plant from crude oil-fuelled to associated gas-fuelled operation enabled PAM to utilize associated gas that was being flared. Four 18-cylinder Wärtsilä Vasa 32 low nox gas (LNGD) engines in V-configuration generating 20 - 24 MW power were converted, and the hand-over to PAM took place in November 2011. Every 1 million cubic foot per day of flare gas optimised for power generating represents approximately 160 barrels of crude oil per day. Thus, PAM expects to save up to 640 barrels thanks to the project. As PAM likes to say: it increased the net crude oil production by an average of one well without having gone through the drilling process.

The PETROAMAZONAS EP and Wärtsilä co-operation succeeded in developing an "in-house" Ecuadorian Project Team and Project Implementation Structure capable of taking a project from an idea to commercial operations. This has been duly recognized by the government of Ecuador, which has now decided that this vehicle should be used to implement energy efficiency projects throughout the country's petroleum sector.

Furthermore, technological solutions were developed and implemented that focused on mitigating the challenges of quantity and quality fluctuations in the delivery of associated gas. At the same time, PAM’s power supply matrix was re-engineered so that today more than 60 MW of capacity has been installed to operate with associated gas. This will be increased to 70 MW in phase three. The other critical technical achievement of the project has been the transformation of isolated power generation systems towards a distributed power system, by installing low environmental impact underground cables.

Wärtsilä's multinational team can reflect on a successfully implemented solution for PAM. It has also created an international benchmark for oil sector energy efficiency and consequently, a business model that focuses on long term sustainable prosperity. 

Carbon Finance

The gas conversion is expected to save over 1Mt of CO2 emissions over 10 years by using previously flared gas for power generation. In parallel with Wärtsilä's delivery of the gas conversion project, the Development and Financial Services group at Wärtsilä assisted PAM in the successful registration of the project under the UN’s Clean Development Mechanism. During the 2 ½-year process Wärtsilä's carbon finance experts guided the PAM CDM team in the CDM registration process, and arranged the sale of Certified Emission Reductions from the project. The income from the Certfied Emission Reductions provides an ancillary income stream for PAM over at least 10-years and was one of the key elements in the investment decision.

Aksa Samsun conversion project

Aksa Enerji Uretim A.S, a part of Kazanci Holding, is one of Wärtsilä’s biggest customers in Turkey. This energy sector company operates diesel and gas power plants, wind farms, hydro-electric plants, solar energy, biogas and landfills, as well as distributing and selling electricity.

The company made an agreement with Wärtsilä in early 2000 for the supply of a 120MW power plant, equipped with seven 18-cylinder Wärtsilä 46 engines, to the Turkish city of Samsun on the Black Sea. The Samsun region has industry, but is also an agricultural area and the local authorities pay considerable attention to environmental impacts. The emission levels from the big factories and power plants were, therefore, of high concern already at that time and the Wärtsilä power plant was equipped with SCR and SOx scrubber systems.

With the tightening of Turkey’s environmental legislation, the company was anxious to convert the engines to use more environmentally friendly fuel. At the same time, however, it had to be kept in mind that the rated output from the engines could not suffer any losses. Additionally, operating costs needed to be reduced to make the plant’s operations more economical. Since the engines were running for only 5000 hours each, only minor modifications to the engines were preferred. Wärtsilä’s suggestion for the challenge was a GD concept, which could cope with all the requirements with improved engine efficiency, yet still be able to provide not only back up fuel flexibility with HFO and LFO, but also natural gas/HFO fuel sharing. As the undersea natural gas pipeline from Russia already exists in the city of Samsun, the set up was clear, and the GD concept was proposed as a means of continuing the plant’s operation under the tight emission laws. The EEQ contract to convert six of the power plant’s engines to GD operation was signed in November 2009, and the project team’s involvement began accordingly. The seventh engine was relocated to Cyprus by Aksa Enerji during the execution of the GD conversion project in order to make room for the first Wärtsilä 50SG engine.

Safety is the driving force

Safety is imperative when using high pressure gas as a main fuel. The fuel oil system, gas detection and automation system, and the fire fighting system were designed according to stringent safety regulations. Different ratings and areas of Ex-zones were determined, and even the access road to the power house building had to be changed due to the compressor house design and location. Ex-proof components were considered for all electrical and automation parts, when located inside the Ex-zone.

A new gas feed arrangement with double wall piping, a new HFO injection system, a control oil system for 370 bar pressure, and a new improved engine control were added to the engine. Basically, therefore, very minor modifications to the engine itself were required.

For external systems, the conceptual design was made through close co-operation between Wärtsilä and Aksa Enerji A.S Uretim. A ‘Safety Concept with a Cause & Effect’ study was made by Wärtsilä and Aksa Enerji based on the Wärtsilä GD concept and local regulations, and this was used as a design and execution guideline. The safety concept emphasizes all the necessary aspects and measures included in the GD power plant concept to achieve an acceptable safety level. 

An optimal gas feed system based on the local conditions was calculated and designed by Wärtsilä experts together with Aksa Enerji A.S Uretim’s gas department.

The gas itself is good quality Russian natural gas with high low heat value (LHV), a low consistence of inert gases, and high methane number (MN). Two high pressure gas compressors supply the six Wärtsilä 46GD engines via an engine wise gas valve skid, which is also able to share the load upon request from the Wärtsilä plant control system. The gas feed piping inside the power house is double walled to enable proper ventilation for the safe evacuation of any possible gas leaks. A reliable, sufficient, and safe gas feed into the engine is an important factor, but the gas blow down and venting cannot be overlooked. Because of maintenance or other planning reasons, the gas flow must be able to be led out (blow down) from the system back to the gas grid. This must be a safe and controllable operation. There is a further need for emergency venting of the gas flow into the atmosphere, which has to be well planned so that it is activated in accordance with the plant controls, etc.

A project specific gas valve skid was tailored by the project team to achieve the optimal reliability and performance for operation with a very low, <2 bar, pressure drop over the skid. The gas valve skids were further located inside the gas tight individual cabinet, which is continuously ventilated and furnished with gas detection equipment that issues a gas alarm in case of any leak or malfunction of the skid.

Testing and commissioning took place in autumn 2011, engine by engine, by the Wärtsilä commissioning team assisted by the Aksa Enerji team. Start up of the GD engine is carried out using LFO or HFO, and then ramped up to 25% to 30% on fuel sharing mode prior to change over to full gas operation with an HFO fuelled pilot. After a few days tuning, the 17 MW was reached with very good heat rate figures. Furthermore, the key issue, the exhaust gas emissions, were accepted by the local authorities, who are continuously monitoring the plant’s exhaust gas emissions via engine wise emission sensors installed on each exhaust gas stack. So, in other words, the production of electricity can continue with far lower levels of exhaust gas emissions, while providing financial benefits through lower operation costs. An additional advantage is that HFO no. 4, or even no. 6, can be used as a pilot fuel to reduce the operational costs even more.

New automation

No conversion project is without a challenge or a surprise of some kind. This is especially true when something new has to fit into an existing environment. The engine and plant automation and monitoring systems were renewed totally, so old panels, sensors, etc were disconnected and removed prior to assembly of the new ones, which were also partly interconnected to the existing systems. In addition, considerable quantities of safety equipment, including detectors, sensors, limit switches, and so on, were installed based on the required safety concept. Once the dismantling and installation work was finalised, the software needed to be updated to the final revision, and once again this was based on the safety concept and the final setting of the equipment.

Overall, however, through close and open co-operation with the customer, the Wärtsilä organizations in Finland and Turkey, and other stakeholders meant that no major surprises occurred - even though the project specific and tailored design was developed during the project itself.

Fuel flexibility

Wärtsilä products are flexible and easily adaptable for utilizing gas as a main fuel. This makes the converting of power plants to gas operation very interesting, for example in terms of lower operation costs, less exhaust gas emissions, fuel flexibility, and short payback time. This is especially important now when the gas grids are expanding and emission levels are being tightened globally. The GD concept requires very few engine modifications, and provides considerable benefits with real fuel flexibility.

 

Wärtsilä Gas Power Plants

Press release

Reference

Fig. 2 – Gas re-injection combined with power generation.
Fig. 3 – W2W: The Waste To Wire schematic process.
Fig. 4 – Associated gas supply characteristics.
Fig. 5–6 – Gas Flaring at Eden Yuturi before and after the GD conversion.
Fig. 7 – Aksa Samsun before the GD conversion.
Fig. 8 – Aksa Samsun after the GD conversion.
Fig. 9 – Pressure testing of the gas pipeline.

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