Toronto: With all the attention being paid to greening the electrical system, another set of environmental initiatives may be going un-noticed: Making the natural gas transmission and distribution system greener. David Teichroeb of Enbridge Inc. has identified a slew of opportunities for greening the gas system, some of which are already underway. With a few regulatory and policy changes here, and some tax code adjustments there, some very significant environmental benefits could be delivered to a country that is a major user of natural gas.
Starting at the gas producer end of the system, Teichroeb sees a number of options for injecting methane from renewable sources into the natural gas pipeline. Biomass, landfill, and various kinds of agricultural and some industrial operations can produce renewable methane, or something pretty close to it, in a variety of locations all across the country. Existing and new technology can be used to purify the gas, which can be introduced to the gas network, and pretty soon you’re shipping renewable energy by pipeline to locations where low-impact energy is most needed.
On high pressure pipelines, as many in the power business know, the compressor stations can be a green energy sources of their own. Waste heat can be recaptured from the compressors and used to produce electricity without any incremental emissions by installing a technology called Organic Rankine Cycle (ORC). In some jurisdictions this kind of recaptured energy is eligible for special programs for renewable energy, even though it’s captured from a natural gas compressor. “Compression and Storage Operations can all be optimized with a shift to new technology adoption,” Teichroeb says.
Further down the pipeline another low-carbon technology can add incremental supplies of electricity. This technology is called a turboexpander and it works by capturing pressure energy from our pipelines and converting this into power. Simply put, natural gas travels great distances through pipelines, and when it arrives in the city the first thing utilities do is reduce the pressure by squeezing the gas through a valve for safe delivery to homes and businesses. Using the turboexpander, the pressure of gas is controlled and useful electricity with low environmental impact can also be generated and delivered to the electricity grid. This is similar to how a water turbine produces hydro electricity. In this case, gas goes in and gas goes out at a lower pressure, and electricity is available for the homes and business in the neighborhood.
Recently, Enbridge commissioned a system in Toronto that improves on the already strong environmental benefits of the turboexpander. It is a 2.2 MW hybrid fuel cell that that integrates a large stationary fuel cell with the turboexpander. The plant’s yearly electricity generation could meet the needs of 1700 homes. Like a battery, a fuel cell operates without burning fuel. It is an electrochemical process that generates electricity from natural gas in the most efficient manner and without smog forming pollutants. “To put things into perspective the fuel cell technology is producing electricity with up to 99% less air pollutants than a typical biomass electricity generator,” said Teichroeb, “but, let me be clear, it not one technology being better then another. Rather we should invest in a portfolio of technologies and use the right technologies in the right application.” An additional benefit of the hybrid fuel cell is the extremely high efficiencies. Greenhouse gas emissions are reduced since over 60% of the hybrid fuel cell’s input energy is converted into the electricity we want, and the heat can still be used in the pipeline process to increase the overall efficiencies.
The story of the greener gas grid is even more compelling if the gas consumer can be set up to operate in ever more environmentally responsible ways. Instead of just burning gas to make heat, many consumers could generate power in distributed generation installations that operate as combined heat and power (CHP) plants. They could extract the waste heat to meet the purpose the gas was originally required for, and use the electricity to power their local needs or sell back into the grid. Frequently the power would be replacing power from fossil-fired generating plants that operate at much lower efficiency and higher emission levels. In some cases the distributed generation can complement intermittent renewable generation, and make it easier for the electrical system to accommodate higher levels of renewable energy.
Now consider the system as a whole. We start with increasing quantities of renewable methane in the pipeline. Technology is installed on the many compressor stations to turn wasted heat into electricity that has a very low environmental impact as we move clean and renewable natural gas across the continent. Next, as the gas arrives in urban centers the pressure is reduced with turboexpanders to generate power in the city where it is needed most. Reduce the pressure with a hybrid fuel cell and the electricity doubles without burning fuel. Utilities have hundreds of these pressure reduction stations, and in some circumstances the same gas passes through two or three pressure cuts before the customer. The same clean, natural gas can generate power up to three times before it is used the most efficient way – in a CHP application that can significantly reduce line losses associated with delivering electricity from central plants.
Teichroeb says, “Opportunity exists for governments to work with the natural gas industry to green the natural gas transmission & distribution grids.” Relatively modest changes would be needed to encourage significant greening of the gas grid. For example:
• Changed government policy can attract capital investment to turboexpander energy recovery, pipeline compressor energy recovery, hybrid fuel cells, etc.
• Policy changes could expand Eco-RP production Incentives to include a wider portfolio of technologies and /or harmonization with the US Investment tax Credit policy for alternative energy investments.
• Energy planning should shift end-users to embrace technology that results in the most efficient use of fossil and renewable fuels as we transition towards a vision where energy production, transportation and end-use have a lower environmental impact. This includes increasing the focus on CHP as we move to smarter energy grids.
Greening the grid may well go beyond electricity.