23 April 2008

Recycled Steam

So I'm in the process of moving (yet again), which has put the brakes on me producing another technical post. So, in lo of that, I think I'll beat on a journalist. Yeah I know, it's like killing kittens, they're just so cute and helpless, but hey, if it helps me vent some frustrations, it's all good.

So I recently read in The Atlantic (home of the esteemed James Fallows) an article by Lisa Margonelli on combined heat and power. In general, this article is fairly good, especially the second half. However, I still saw some paragraphs that rankled. Let's dive in, shall we?
The U.S. economy wastes 55 percent of the energy it consumes, and while American companies have ruthlessly wrung out other forms of inefficiency, that figure hasn’t changed much in recent decades.
and, later,
For the better part of a century, we’ve gotten electricity from large, central generators, which waste nearly 70 percent of the energy they burn.
A ha! Yes, the ever popular confusion regarding the difference between useful work and waste heat. Once is forgivable as editorial discretion, but twice is a pattern. Let's take nice, high-pressure and hot steam and pass it through a steam turbine. Surprise, we lose heat and pressure from the steam in order to run the Rankin cycle. You can take that steam and pass it through another turbine, but the 2nd cycle will get a lot less electricity out for the same capital costs. The final potential use then is to take the latent heat from the low-quality steam and dump it somewhere: process heat for drying , heating the factory floor, or speeding up some chemical reaction.

Ok, so definition time: this article is about combined heat-and-power (CHP), but you won't see those words in this article. In fact, the article only talks about the other way around — capturing waste heat to make electricity.

CHP usually aims to take an industrial activity where you burn a fossil fuel for process heat, and run the fuel through an electricity generation process first and use the waste heat for the process. Margonelli, on the other hand, provides an example where electricity is used for heating. This isn't common, because electricity is still far more expensive than natural gas on a pure dollar per Joule basis. In fact, it's only used when you need either extremely high purity or extremely high temperatures. Such as,
Heat, which in some industrial kilns reaches 7,000F, can be used to produce more steam.
tungsten tool making for one. Needless to say, most industrial activity isn't involved in the manufacture of refractory materials, zone-refined silicon, etc. This is my major problem with the article. The example provided isn't very representative of industrial uses of heat. What can be economic for a specialty steel refiner probably isn't for an ethanol plant or oil refinery.

TANSTAAFL (There Ain't No Such Thing As A Free Lunch) applies here as much as anywhere. For some plants, better insulation may be a better buy.
In some industries, investments in energy efficiency also suffer because of the nature of the business cycle. When demand is strong, managers tend to invest first in new capacity; but when demand is weak, they withhold investment for fear that plants will be closed. The timing just never seems to work out. McKinsey found that three-quarters of American companies will not invest in efficiency upgrades that take just two years to pay for themselves.
This says a lot more about business leaders' acumen than the particulars of a efficiency upgrade. If you can't generate some cash flow to invest in capital equipment (and that is what we are discussing here — a gain in productivity) during a boom you probably aren't going to survive the inevitable bust. Why the emphasis on capacity growth? Are the CEOs really that concerned about losing market share? Or is this just an example of knee-jerk brownian attitudes? Or are executives just really dumb? (Don't answer that.)

The other giant impediment to CHP the article sort of dances around but never really addresses. In the giant race to the bottom of labour costs (i.e. off-shoring), it is a pretty big gamble for a power plant to setup for combined heat and power and then hope that their customer will still be around in five years. Low-grade steam isn't something you can pump around the state to find a new customer because you'll simply bleed it all off as parasitic losses to the pipeline. So I think the emphasis on Free Trade which has introduced such volatility in the cost of labour is probably a big part of the general failure of CHP to have a big impact on our energy economy.

The other reason CHP hasn't really taken off is that natural gas hasn't turned out to be as cheap or as fungible as expected, and it's the only fossil fuel that's really clean enough to run with decentralized power and easily pipelined. Coal isn't.


Fat Man said...

My computations based on:

From Bloomberg.com:

Residual Oil @ $3.30/gal
Nat Gas @ $11.00/MMBTU
Electricity @ $84.90/MWh

And Residual oil 38.7 MJ/l from wikipedia

I get:

Residual Oil $22.53/GJ
Nat Gas $10.43/GJ
Electricity $23.56/GJ

No quality of service factor in those prices.

I think gas is the underpriced commodity, but it will be coming up in the near future.

Robert McLeod said...

If natural gas closes up with oil we should see some coal-to-gas projects. It's relatively straightforward to gasify coal, and converting the synthesis gas to methane isn't super-hard either.

If we ever do get to the point of electricity being the cheapest, we can probably look forward to a lot of electro-slag refined steel products. It would take a carbon tax.

Krassen Dimitrov said...

"The other reason CHP hasn't really taken off is that natural gas hasn't turned out to be as cheap or as fungible as expected, and it's the only fossil fuel that's really clean enough to run with decentralized power and easily pipelined. Coal isn't."

Isn't that the best argument for CHP? If I am a small gas-powered generator, and gas-prices are killing me, what do I do? I make steam with my waste heat, and...? Setting up a second (steam) turbine cycle is expensive and often you need scale (several gas turbines per steam turbine are required.
If I could sell the steam to somebody: a municipality for home heating, or an industrial customer, then I am better off.

Robert McLeod said...


Natural gas is expensive compared to coal. CHP is fairly useless for a peaking power plant.

Engineer-Poet said...

Scrubbed syngas (from coal or biomass) is as clean as natural gas, and can be pipelined some distance from the point of generation.  It also has some potential for storage.

Cyril R said...

If the gassification is done underground in a controlled manner, it's possible to leave much of the undesireables deep underground. Cheaper, more abundant lower quality coal types can be utilised in a clean manner.

It's hard to get away with the GhG emissions though in the future, IMHO.

Anonymous said...

Surely the point of the Article "Waste Not" is that recycled steam is an ecologically sound concept. All your arguments about costs of comparative fuels, will amount to a "hill of beans" in the grand scheme of things, when we're all dead from global warming.

I would say that it is also true that it takes less energy to re-heat 'recycled steam' to make it higher in pressure (there's also a man out there with a pump to do it) than it does to make 'fresh steam' from scratch with cold or frozen water. Any school child knows that, so why don't energy companies?

Whether Coal; Gas or Oil fired; power stations have wasted millions of tons of the worlds fuel rescources in the last 60 years since the war. Has anyone ever calculated how mauch was wasted during the two World Wars and other skirmishes of the 20th Century either? We're still at it too.

The Universal Declaration of Human Rights in 1948 spoke of all the people of the world benefiting from new technology, but they haven't have they? Wake up and smell the coffee and campaign for a better world as money is worthless now thanks to the greedy selfish Bankers and Entrepreneurs.