Norman Rubin

November 21, 1997

  Select Committee on Ontario Hydro Nuclear Affairs Attention:
Derwyn Shea, M.P.P., Chair (Fax: 416-314-7783)
Doug Galt, M.P.P. (Fax: 416-323-4439)
Sean Conway, M.P.P. (Fax: 416-325-9001) Dear Committee Members: In your deliberations yesterday, you asked Dr. Nigel Roulet to quantify the relative CO₂ emissions of the various forms of fossil fuel generation, but he did not have those quantities in his head. You finally referred the matter back, I believe, to the Chair and the staff, to seek an answer. In the interests of assisting your deliberations quickly, following are some "quick and dirty" numbers that are generally used in this field:

• Coal combustion releases twice as much carbon (or carbon dioxide) as natural gas combustion, per unit of energy released, all other things equal.
• Oil combustion is almost exactly halfway between the two.
• While all fuels are generally burned at comparable (and fairly high) efficiencies in electricity generation, the "thermal efficiency" — i.e., the percentage of the flame’s heat that actually becomes useful energy (electricity) — varies widely. As a result, fuel consumption and atmospheric emissions can vary widely, for the same amount of useful energy provided.
• Large, centralized steam turbines like Ontario Hydro’s (whether coal, oil, gas, or even nuclear) typically convert roughly 30-33% of their fuel’s heat into electricity. The remainder, roughly two-thirds, is released to the environment — through the stack and as "condenser cooling water" to the adjacent lake.
• New off-the-shelf natural gas technology (combined-cycle gas turbines or CCGTs) now convert well upwards of 50% of their fuel’s heat into electricity. In a simple or "stand-alone" CCGT, the remainder, roughly half, would be released to the environment, as above.
• Even more efficient are industrial or municipal cogenerating plants, which replace the combustion of (typically) natural gas for heat, and may also supply cooling, derived from that heat. These plants may use any one of several technologies including CCGTs, and almost always turn at least 75 or 80% — and often over 90% — of their fuel’s heat into either electricity or commercially useful heat. (The ratio of electricity to heat is variable from about 1:5 to about 2:1, and is typically optimized to maximize the value of the return to its owners.)
• Since the economic (and environmental) benefits of natural-gas-fired electricity generation are generally (1) available at relatively small scale and (2) maximized when the generation can be sited where there is a demand for heat, they are generally more attractive to "customers" and "non-utility generators" than to "utilities" like Ontario Hydro. Technically, of course, there is no reason why a centralized utility like Ontario Hydro could not construct CCGTs at its own sites.

Perhaps the best way to summarize the combined effects of the choice of fuel (which you gave some attention to in yesterday’s hearing) and the even more important choice of technology (which was not mentioned in that discussion) is with the following simplified example. Let’s assume that a large commercial customer has a large demand for electricity and a simultaneous demand for twice that quantity of thermal (heat) energy, or its equivalent in cooling. At present, that customer is burning gas to meet its thermal load and buying electricity.

If 100% of that electrical demand is supplied at Ontario Hydro’s coal fired stations (at 33% thermal efficiency), let’s call the resultant CO₂ emissions 1000 units. (The units are arbitrary, as long as we’re consistent.) If Ontario Hydro uses an oil-fired station, the CO₂ emissions would drop to about 750 units. If Ontario Hydro uses a gas-fired station (like the Hearn G.S.), CO₂ emissions would drop to about 500 units. If either Ontario Hydro or the customer or a "non-utility generator" generated the power with a CCGT at 50% efficiency, CO₂ emissions would drop to about 333 units.

But in all these examples, the customer is burning natural gas to supply its heat load, which is twice the size of its electrical load. Assuming 80% thermal efficiency for that gas combustion in a boiler or furnace, it would result in roughly 416 units of CO₂ emissions, all additional to the emissions from the electricity generation. The total CO₂ emissions, from supplying the customer’s electricity and heat needs, would range from a low of 749 units up to a high of 1416 units, depending on the choice of generating fuel and technology.

 If, on the other hand, the customer chose to install a gas-fired cogeneration unit, converting one-third of its energy into electricity and two thirds into heat, its total emissions would equal 500 units — a full 33% lower than the most efficient case dealt with above! Looking at it a little differently, the electrical generation part of this cogeneration application only emits 74 units of CO₂, over and above the 416 units of CO₂ emissions from the boiler or furnace. That is almost five times as "emissions efficient" as the CCGT option above, the most efficient option discussed. Looked at still another way, if the customer’s electricity were generated from a "mix" of sources — nuclear, hydroelectric, and coal — that "mix" would only have to contain tiny 7.4% of coal-fired generation to exceed the total emissions of the cogeneration alternative! (For simplicity, we are ignoring the CO₂ emissions from building the generating stations — including the hydro and nuclear ones — and mining fossil fuels and uranium, etc., as well as the potentially very large emissions of the potent greenhouse gas methane from hydro dams that submerge living plants.)

Incidentally, since the estimated CO₂ emissions for our gas-fired cases are exactly proportional to the natural gas consumed in those cases, we can see that the more modern, more efficient, more decentralized technologies also have significant benefits in saving fuel — an economic advantage to the customer and presumably to future Canadians as well. The CO₂ emissions results (again, in arbitrary units) from these admittedly simplified cases can be summarized in the following table:

These examples are only illustrative and approximate, but I believe they indicate both the significant environmental benefits of choosing natural gas instead of coal, and the equally significant benefits of encouraging distributed, decentralized, super-efficient — in short, non-monopoly — use of that natural gas. Of course, the examples could just as easily have been industrial or municipal (like the cogeneration developments Ontario Hydro is currently opposing in the Courts) rather than commercial. I hope this is helpful, and good luck in your deliberations. Sincerely yours, Norman Rubin
Director, Nuclear Research and Senior Policy Analyst cc: Donna Bryce, Clerk (Fax: 416-325-3505) 1. Assuming 50% of the mix is nuclear, 25% of the mix is hydroelectric, and 25% of the mix is coal-fired. We also assume that nuclear and hydroelectric generation create no CO₂ emissions at all, as discussed above. Furthermore, we do not include any fugitive emissions of methane from (changes in) natural gas consumption.