Howard Bell, Commercial Applications, Mercury Electric Corporation, Alberta, Canada
The Western Canadian Sedimentary Basin is Canada’s primary oil and gas producing area. Much of this activity is concentrated in Alberta, producing 2.5 million barrels of oil per day and 353.8 Million m3/day of natural gas. Gas flaring has become a major environmental issue but Mercury Electric Corporation has found a way to combat the problem and transform it into an energy making project.
Mercury Electric Corporation is an independent power producer (IPP) based in Calgary, Alberta, Canada. The Company’s focus is on small scale on-site power generation in the oil and gas industry, as well as the commercial and light industrial sectors. Mercury is the exclusive Western Canadian distributor for the Parallon 75, a 75 kW microturbine manufactured by Honeywell Power Systems Inc.
Mercury has taken delivery of more than 50 Parallon 75 units since April 2000. Of considerable note is the recent installation of 38 Parallon 75 units at eight separate oil production facilities in Northern Alberta. The microturbines are being operated as baseload units running parallel with the distribution grid. The unique aspect of these installations is that the microturbines are using flare gas as fuel. The electricity produced is being sold hourly on the spot market through the Power Pool of Alberta.
Mercury’s microturbine power solution offers oil and gas companies an economic means of reducing solution gas flaring, a burning environmental issue in an energy rich but power deficient province. Mercury Electric Corporation anticipates installing hundreds of Parallon 75 microturbine units in flare gas applications over the next few years and will soon begin applying this technology in powering remote oil production facilities, and developing previously uneconomic shut-in gas reserves.
The current flaring situation
In general, the majority of flaring occurs at oil production facilities at which gas is a by-product of oil production. This is commonly described as “solution gas” which generally has a high BTU content and varies widely in composition. Common constituents which must be removed in order for the gas to meet pipeline specifications are: water; hydrogen sulfide (H2S); carbon dioxide (CO2); and nitrogen (N). In addition, certain heavier hydrocarbons such as ethane (C2); propane (C3); butane and (NC4 and iC4); and heavier hydrocarbons (C5+) are often entrained in the gas and will condense out as pressure increases or temperature drops.
Figure 1. Mercury has taken delivery of more than 50 Parallon 75 units since April 2000
With 94 per cent of all solution gas captured and produced into pipelines, Alberta has an enviable conservation record compared with other oil producing regions. However, the six per cent that is not captured results in approximately 2.94 m3/day of natural gas being flared at more than 4000 oil and gas facilities. This wasted energy, if converted to electricity, would generate over 200 MW of baseload power. Though significant in aggregate, the solution gas volumes flared at any given location are too small to economically capture, refine, and compress into the main pipeline system. The oil production facilities are either too far from a natural gas pipeline or are located in an area where there is no spare gas plant processing capacity. In certain cases, it is just too expensive to remove the impurities from the gas in order for it to meet the required pipeline specifications.
Flare gas combustion
Currently, most flare stacks, especially older units, are quite poor at achieving a high degree of combustion efficiency. An Alberta Research Council study undertaken in 1996 concluded that flare stacks only burned 64 – 82 per cent of the gas stream, leaving a substantial proportion of hydrocarbons either unburned or partially combusted. Though this study indicates the need for more research, it is clear that partial combustion of hydrocarbons results in the formation of up to 250 different volatile organic compounds.
Figure 2. Alberta has an enviable solution gas conversion record
Given the wide variation in gas composition, heating values, temperatures, and delivery pressures, it is necessary to use robust combustion technology to achieve a high degree of combustion efficiency. Turbines by their nature should exhibit these qualities since they burn the gas in an internal combustion chamber at relatively high temperatures with large volumes of excess oxygen present. Independent emission sampling indicates that the Parallon units attained combustion efficiency greater than 99.5 per cent using raw solution gas. Microturbines therefore have demonstrated the capability to dramatically reduce emissions and turn a wasted resource into useful energy.
Converting the resource
As an Alberta-based IPP, Mercury recognized the opportunity to capture this wasted resource but needed to find the most appropriate technology for this challenging application. Though solution gas is typically flared in continuous streams, the volumes are often too small to employ conventional turbines. In addition, the most recently developed oil reservoirs in the Western Canadian Sedimentary Basin have a relatively short production life. As oil
production at a facility starts to decline, gas production also falls off, and experience indicates that it is often uneconomic to put larger turbine equipment with their associated fixed infrastructure at a site for less than seven to ten years.
Mercury has identified microturbines as the most promising technology for solution gas power generation because of their low fuel requirements, relatively high simple cycle efficiency, and robust combustion capabilities. Having the flexibility to use smaller scale turbine technology to capture this “waste” product offers a real breakthrough for solution gas conservation. This is particularly applicable to solution gas flare sites with small and declining volumes of gas where the relative portability of microturbines offer the flexibility to adjust the number of generating units to the fuel supply on an ongoing basis.
However, as the technology is still in its infancy, it is critical to prove that microturbines are capable of operating reliably and effectively on raw gas in isolated areas under challenging field and climatic conditions. Alberta is the ideal testing ground for the following reasons: electricity deregulation has provided a market for the electricity produced from flare gas; there are ample sources of waste gas and entrepreneurial companies are prepared to take a chance on new technologies; and a robust three phase utility grid system has been developed throughout most of the oil and gas production areas.
The Parallon 75
Figure 3. The 75 kW Parallon consists of three primary components
The Honeywell Parallon 75 is a high speed microturbine generator with an output of 75 kW. The Parallon consists of three primary components, a core engine, a recuperator, and the power electronics. The core engine is a high speed turbine, operating at approximately 65 000 r/min at full output. The core has only one moving part, a single shaft with the compressor, expander turbine and permanent magnet supported by journal and thrust air bearings. An oil circulation system provides cooling for the power electronics and the generator stator. The air bearing design eliminates the need for oil lubrication. The 28.5 per cent electrical conversion efficiency is attained by feeding the hot exhaust gases through a heat exchanger known as a recuperator, and passing this energy to the compressed inlet air. The modular design allows for the entire engine core to be easily exchanged in the field for a factory rebuilt unit. The turbine engine is operated by a dedicated computer that can start the turbine, monitor and protect it and match the power output load to the most efficient engine speed.
The permanent magnet mounted on the cold end of the shaft rotates in the stator which then outputs power at a frequency in the range of 1000 Hz to 1300 Hz.
To be able to economically generate baseload power in simple cycle operation, three issues had to be addressed; low cost installation, operating, and maintenance. Because of the need to relocate units as gas volumes decline, it is also necessary to maintain portability of the balance of plant to minimize stranded infrastructure. Based on our prototype testing experience, it is desirable to minimize field labour, as the cost and timing of construction and maintenance is magnified in these often remote locations. Therefore, all preparation which can be undertaken prior to shipping units to site is done in our Calgary facility. Likewise, the ability to monitor, control and download meter information using Scada saves a great deal of time and money.
Our current projects range in size from a single 75 kW unit at the Husky Energy Nipisi Oil Battery to a Numac Energy facility which has sufficient gas to support nine Parallon units. In evaluating the market opportunity, Mercury determined that a large number of sites had sufficient gas to operate at least three units. Based on this, Mercury has developed a standard three unit generating plant, mounted on a heavy duty steel skid, which is readily transportable and rugged enough to withstand oilfield conditions. This prepackaged skid minimizes the need for significant site preparation or construction.
Each generator is equipped with a delta/wye isolation transformer for safety and proper utility isolation. Utility interconnect requirements dictate that a visible disconnect be supplied that is rated to break the maximum power output for each site. An electronic power meter with 15 minute interval recording and 40 day storage capacity is included with each generating plant. The meter can be remotely accessed and serves as the project cash register. The Parallon units and associated switchgear are all designed for outdoor use, and as such the skids do not need to be enclosed within a building. This results in cost savings and permits the skids to be small and light enough to transport without special accommodation such as pilot trucks or restricted hauling times.
Because the Parallon is designed for single phase fuel flow, it is necessary to ensure that all fuel remains in a gaseous state throughout the fuel delivery process. With temperature and pressure changes occurring through the piping and compression process, the raw solution gas normally requires conditioning to knock out free liquids and any solids which may have carried over from the crude oil. This has been achieved in a cost effective manner by employing scrubbers and filters both prior to and after the fuel compressor. These scrubbers and filters are mounted on the skid and have auto-dumps to dispose of liquids into a discharge line usually going to the facility flare knock-out drum or back to the treater.
Utility interconnect issues
In Alberta, the distribution wire owners have not previously encountered interconnection with inverter-based generators. Islanding of the generator usually heads the list of concerns, followed closely by interference with the inline reclosers and other protective relaying. The Canadian Standards Association (CSA) electrical code specifically regulates generators against “feeding into a fault” on the wires system. In addition to the protective issues the generators must meet the power quality standards for harmonic distortion and voltage regulation. All generators, including inverter generators, must be equipped with the standard over/under voltage, over/under frequency and instantaneous overcurrent protection. Timed undervoltage is not required but is helpful to both the utility and the generator in riding through momentary voltage sags.
Figure 4. Mercury has installed the standard three unit generating plant at a large number of sites
Mercury has worked closely with the utilities in Alberta to educate them on the inherent operating characteristics of inverter based generators. The two major wires owners in the rural areas, Utilicorp Networks (formerly TransAlta) and Atco Power have been very cooperative in working with independent power producers to develop appropriate interconnect guidelines which recognize the nature of the generating technology. The resulting guidelines are significantly less onerous than to interconnect either conventional synchronous or induction generators. These guidelines will encourage producers to look at reducing solution gas flaring further over the next few years. Mercury has now successfully interconnected Parallon 75 units to all of the major distribution utility systems in Alberta, and interconnect agreements generally take less than three weeks from application to signature.
The small scale nature of the generating plant and limited site requirements allow for a short installation and commissioning cycle. All sites served to date have three phase 25 kV distribution lines to the edge of the oil facility lease. Where the
25 kV/480 V utility transformer was sufficiently sized to accommodate the volume of power being exported from the generating plant, Mercury was able to tie in to the low voltage side. At facilities where the transformer was too small to handle the plant output, an additional transformer has been added, and then connected to the distribution system at the closest available power pole.
Depending on the oil production facility, piping either runs above ground on racks, or underground in trenches. The piping changes required to provide fuel for the generating plant are minimal in nature and have no impact on the operation of the oil production facility. Piping changes normally take only a few days to install.
Communication methods with the
on-board Scada varies depending on whether the site has an existing land line or cellular coverage. In extreme cases, satellite communication can be used although it is very expensive. All projects to date have used either CDPD modems or regular modems which communicate to proprietary Mercury master station software.
Mercury Electric Corporation’s first project installations took longer to commission than anticipated due to liquid removal issues. By incorporating our knowledge and working with the oil producer, this commissioning period has been shortened to less than a week.
Mercury expects that the Parallon-based IPP offering will assist companies to achieve their flare reduction targets without diverting their capital and human resources from their core activity. The viability of this technology bodes well for future power projects at the over 4000 flare sites in Alberta, and other major oil production areas around the world where solution gas is routinely flared.