In the Push for Alternative Energy, What Happened to Geothermal?

t281a

c640t

I think this article highlights one of the fundamental differences between what is possible and what is feasible and scalable with current and near future technology. In essence the difference between science and engineering.

Scientists tell you what is possible, what the laws of nature are and what they allow or don't allow. Usually these are in very general terms, nothing too specific. Engineering on the other hand tells you what is feasible with current and near future technology.

Let's take electromagnetics for example. Maxwell developed the equations of electromagnetism back in 1862 and showed that electromagnetic waves travel in space. These are the exact same equations we use (or derivatives thereof) to construct the wi-fi circuitry in your computer, the circuitry in your cellular phone, in your DVD player, computer, VCR, radio and TV. Though Maxwell could tell you that you could use Electromagnetics to transmit information, he could not tell you how to construct a TV. That's the difference.

Scientists can tell you what is possible, but they cannot tell you in detail HOW to make it possible. The details are left to the engineers.

The power of big coal

The lack of funding for geothermal comes from pressure from the coal industry at the very top levels. EGS geothermal could totally replace coal so research money is instead wasted on harmless follys like hydrogen which can't hurt the fossel fuel business. Geothermal is already cheaper than the coal in the West if you deduct the subsidies and hidden costs. Research on deep hard-rock drilling could make geothermal practical even in the Eastern US but they are spending nothing on research.

Please read my articles on geothermal at www.clrlight.org

Re: Malcolm Kass

Re: Malcolm's comment, I would like to offer the perspective of my education as a geological engineer, and I would advise Malcolm that not everybody in the geological science community has their heads as far up in the clouds as you would perceive. I know you're not poo-pooing on geologists, but your sweeping generalization leans towards hyperbole.

As someone who is conducting active research into this topic, I think I would like to offer my views on some of your points. As I am a geological engineer and I don't know everything about thermodynamics, similarly, you are a chemical engineer and may not know everything about geology.

"First, we do not drill ten of thousands of feet down for oil" -This is a rather linear thought, I'm assuming that the argument here is that you MUST go deeper to reach threshold temperatures for geothermal electrical production. Even in sedimentary basins, where there is abundant data available on down-hole temperatures, temperature anomalies may differ widely from the typical 30 C /km range. Binary heat exchange technology is used to capture marginal geothermal resources (such as electrotherm's green machine) and the amount of heat available for extraction is dependent on the delta t between the formation fluid temperature and the condensing temperature of a working fluid. With a delta t of at least 80 degrees, based on current thermodynamic efficiencies, taking into account pipe friction, pump efficiencies and many others, it appears feasible to produce GT electricity at a US market price. That being said, if in an existing oil well there is an anomalic temperature of 100C at a depth of 3000m, (not unreasonable) and there is a cooling source available such as a lake in close proximity at 10C, it appears that thermodynamically economical production is possible if you keep your well re-conditioning costs under about a million dollars.

Secondly, there is absolutely no need to run engineered chemicals down into the borehole to collect the heat from the subsurface. Yes, somewhere along the line something has to vaporize, which is why a heat exchange system (like forementioned green machine) contains a benign amount of vaporizing fluid which is converted into useful work, and eventually a load. In fact, it is advantageous to use the existing formation water because it can be injected in a dispersive pattern in the reservoir, where it has high carrier to surface area contact, produced up to a heat exchanger to transfer the energy, and then reinjected without ever being exposed to the surficial environment, hence posing minimal environmental threat.

Yes there are some pretty nasty and corrosive chemicals in some reservoirs, namely CO2 and H2S which are hazardous to well equipment. However, one can mitigate this problem by prodcing from a clastic reservoir instead of a carbonate reservoir; clastics have a mineralogy that is less conducive to the production of corrosive agents.

I hope this helps the discusn along.

There is more to this "lack of discussion" than you think

From an engineering point of view (chem. eng., the type of engineer that would actually deal with something like this), I think there is probably a very good reason for the lack of discussion.

While geologists may know the thermodynamics behind this, what they do not know is the physics and material constraints on such a project. Trust me, I am not being negative, or poo-pooing on geologists, but they are not educated in terms of physics and the constraints. First, we do not drill ten of thousands of feet down for oil. Off shore rigs may go down that deep, but drilling thru a mile of water is a smidge easier than rock. Seconds, the types of chemicals that would be best of vapor pressure conditions are very expensive and many of them are very dangerous to use. Third, one needs to ensure the piping doesn't leak. I promise you that is borderline impossible. The piping for oil well leak alot, but that is ok for the oil just drains back into the oil source. But for these conditions, you must have the chemical not leak, for if it does, you lose everything, the heat transfer, the vapor generated.

Anyway, all that I am trying to say is that geologist only know part of this problem, the thermodynamics. But the reason engineers get a salary premium over scientists is that many times the science is far easier than to actually build something that works. Geologist really need to discuss these issues with engineers and material scientists to get the whole picture of the problem.

In most of the USA, the geothermal gradient is about 1.4 degrees F per 100 feet. The rocks get hotter by 1.4 degree F for every 100 feet deeper you go. Some volcanic areas are of course much hotter, and those are the good candidates for dry or wet geothermal. But at 1.4 degrees, at 20,000 feet depth, you get a rock temperatureof about 280 degrees F (plus add about 55 degrees for average near-surface temperature) and you get 335F. Of course, if you start taking heat out, the 335 cools pretty quickly, and it probably cools pretty quickly anyway on it way to the surface.

So, you really have to drill a lot deeper than 20,000 feet to get sustainable higher temperature. Some oil wells have gone that deep or deeper, but most oil wells are 12,000 feet or less. For good reason, at those depths and deeper, the rock is so hot that crude oil breaks down into its constituant parts, i.e. natural gas, propane, butane, others. Drilling a 20,000 ft well costs a LOT of money. You would have to drill a whole field of them, and alternate taking heat from some wells, while others would be given recovery time. In hot dry rock, you would have to pump water down some of the wells to be heated and recovered as steam from other wells.

In some ways, hot dry is better than natural wet rocks (i.e. geyser/hot springs sources. The hot water that has lain for thousands of years in the deep earth rocks have dissolved many minerals, some quite nasty, sulpher compounds and others. As they rise to the surface, the pressue and temperature drop, and these minerals deposit out, clogging your well and your drill pipe. These compounds are usually also quite corrosive, and will rust your drill pipe and other equipment ie.e turbines or heat exchangers. Hot water injected into hot dry rock would not have these problems to nearly the same degree (less dissolved minerals).

Also, if you drill REALLY deep, into REALLY hot rocks, the rocks begin to get a bit soft, and will exhibit plastic flow, whereby the drill hole slowly deforms and closes off.

Never-the-less, the energy is there, but it would be pretty expensive, except less so for those areas (western USA) where there has been near-surface magma flow (hot dry rock). that has heated the rocks not-so-deep. Ken Geologist.

geothermal energy

Carl,

I agree- the lack of discussion makes no sense at all- this is a viable replacement for baseline power in the US.

We need to make the investment in this technology ASAP- it is clean and the fuel is free, once the plants are up and running.

There area few companies involved in Geothermal plant development (mostly small and relatively new) in the US. They may very well be the key to the US's clean energy self-sufficiency in the next 10 years

Dry Geothermal

I am an Electrical Engineer, no expert on energy, however. The magazine of my professional association (IEEE Spectrum) recently published a lead article on the various types of alternative energy sources.

I was shocked that dry geothermal (pump water down to hot rocks, then use the steam that is returned to generate electricity) had by far the greatest energy production potential, and the least public discussion. There was an assertion (if memory is accurate) that it could supply all current electrical energy use for 10,000 years, not just 20%

I googled the subject and found that U.S. scientific articles dried up in the mid-nineties, but that other countries (especially Australia and Canada) were pursuing active production efforts.

If nuclear is too dirty, wind and solar to erratic and small, ocean untried, where do you go? Yes, the drilling is expensive, but we're only talking about 4-5 5000 foot wells per plant when we routinely drill many holes tens of thousands of feet long for oil. Hot rock beds supposedly exist under most of the continental U.S. and I would guess that existing coal electical plants might be retrofitted.

The lack of discussion makes no sense.

Misstated Numbers

While it is good to see Geothermal receiving more media attention, the numbers stated in the article for current production are not correct.

Geothermal, Solar and Wind make up less than 1% of US energy production - combined.

http://www.eia.doe.gov/cneaf/alternate/page/renew_energy_consump/rea_prereport.html

(Tables 1 and 4 in particular.)

Trouble

Any article that is mostly about government funding is a dead give away that there is no there there.