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Mining E

Transport only the end product - Electricity
  [vote for,

Transform the mining for electric power generator fossil fuels into a subsurface process to produce electricity directly. Fit a remotely operated tunnel boring machine (TBM) with a fuel sorting preprocessor, a furnace, generator, and carbon dioxide scrubber. Instead of strip mining coal or pumping up crude oil and then shipping that about for processing the TBM would have appropriate preprocessing elements that then feed a furnace element which drives the generator. The TBM would be unidirectional with limits in steerability. The tail end on the TBM would consist of an umbilical that would carry the electric power to the surface. Additionally the umbilical might include a tube to be used to pump air down for feeding the furnace or a tube for carrying cooling fluid to keep the umbilical and processing components within operating norms. The TBM would progress through the ore as required to provide fuel for the furnace. A seal would be managed around the umbilical so that any waste would be sequestered underground.
dataloss, Aug 27 2015

Using coal fires Make_20use_20of_20coal_20fires
No mechanism. [bungston, Sep 02 2015]

LOX http://world-nuclea...Coal--Technologies/
It appears liquid oxygen is used for some clean coal generators. [dataloss, Sep 03 2015]


       When coal is mined as per this Idea, a major waste will be carbon dioxide. If you don't specify a way to lock it underground away from the TBM, you will need to provide a way for it to reach the surface, else it will smother the combustion of more coal.
Vernon, Aug 27 2015

       I don’t know the details of how the carbon dioxide scrubber works but I was under the impression that the carbon dioxide could be converted to a form that would be left in the ground. Or did I miss something simple like volume of coal burned is less than the waste ash and the exhaust gas produced? Are you suggesting that the exhaust gas will need to be pressurized and contained in order to keep it underground? The air intake for combustions is to be pumped from the surface through the umbilical.
dataloss, Aug 27 2015

       Theoretically creative & feasible.[+]   

       In practice / engineering, it'd be rather difficult, for many of the reasons you already covered are expensive to pull off & not very robust.   

       For example, most of the material you bore will be waste rock, with just seams of coal or other target fuel. Usually, they crush the rocks & separate out target material from waste/byproduct. That separation process may be rather uneconomical to do on a moving, subterranean head.
sophocles, Aug 28 2015

       Imagined it as a mole simply bypassing the material until the TBM reached the target seams at which point the furnace and electric generation begins. Perhaps only certain geological structures and seam sizes might make the economics work. Then again how much of an economic advantage might a TBM system need in order to best the massive cranes, gigantic trucks, and long trains used in strip mining operations?
dataloss, Aug 28 2015

       What happens to the poor seal?
MaxwellBuchanan, Aug 29 2015

       I'm not sure, perhaps she was broke.
dataloss, Aug 29 2015

       sophocles - Browsed the web a bit on seam sizes and they can be massive 6 meters thick and miles long. Some of the images showed a fairly clean looking raw coal. A longwall mining machine can cut 26,000 tons a day. A 500MW power plant consumes about 3,000 tons per day. I would expect that the TBM power output would be scaled down quite a bit.
dataloss, Aug 29 2015

       Coal is normally processed in "washing plants" before being shipped off to the power station. Moving the heavy, bulky machinery of the washing plant along the coal seam would probably use more energy than moving the coal to a fixed washing plant.
pertinax, Aug 30 2015

       Subsurface furnaces look even better after reading up on Coal Preparation Plant (CPP or CHPP if handler included). Much of the process is done to prepare it for transport. Transportation costs make it desirable to remove as much of the waste material as possible. Why? The waste material lowers the energy producing volume while at the same time increases the ash produced during the burn. The ash must be disposed of which adds another layer of transportation costs and wasted energy. Most of what the CPP does would not be necessary if Mining E could be done. The ash exiting the TBM would likely have a greater volume but it should not matter because for the most part it will remain where it original was in the ground. Overall the TBM would eliminate the wasted energy of transporting the waste material to and from the CHPP because we are not overly concerned about the waste in the ash. One other improvement is that we can eliminate the wasted energy and cost of transporting and handling the ash.   

       But we still have the problem that Vernon pointed out - “smother the combustion” My wishful thinking had me see the lump of coal as a solid and heavy so it had to be more massive than the air that was used during the combustion. Ignorance is bliss and then embarrassment sets in at the realization that at a minimum more than twice as much mass of oxygen is required for the burn. But wait there’s more - to get that much oxygen from ordinary air we will need about four times more mass of air since it is roughly a quarter oxygen.   

       Time for a revision - need to consider an alternate oxidizer with denser oxygen content and then revise the umbilical to provide and export path of an equal volume to that of the oxidizer … maybe coal? BBQs anyone?
dataloss, Aug 30 2015

       What form does that carbon take, post scrubbing, and how much energy do we net?
WcW, Aug 30 2015

       Now there's a idea, [dataloss]. Summer barbecuing season could yield a reasonable amount of electricity if we all had cogenerating barbecues.
normzone, Aug 30 2015

       No luck yet in finding specific power consumed by individual elements so I don't yet have a power advantage estimate. The following table (not sure that will fly on this site) includes what I was trying to isolate:   

       Mining E TBM vs LongWallMining Conventional Coal Generator   

       TBM LWM   

       -y- -y- Cutting head   

       -y- -y- Furnace   

       -y- -y- Scrubber   

       -y- -y- Generator   

       min -y- Furnace feeder conveyor   

       --- -y- Conveyor belt out of mine   

       --- -y- Transport rail/truck   

       --- -y- Coal Processing Plant   

       --- -y- Ash handler transport   

       -y- --- Concentrated oxidizer (likely will result in higher power output so this may not be a burden)   

       One time costs   

       --- -y- Surface facility   

       --- -y- Surface roads   

       --- -y- Surface rail line and rail cars/trucks   

       -y- -y- Consider the building of a TBM is equal to that of a LongWallMining machine
dataloss, Aug 31 2015

       From a chemical perspective how are you going to fix the carbon? No such technology exists today that allows for stabe fixation and also yields much energy.
WcW, Sep 01 2015

       A hydroponic TBM, sweeeeeeet. Almost interstellar.
wjt, Sep 02 2015

       Get linking, Vernon. I know you have an idea about using the spontaneous underground coal fires to generate electricity and at least one alternate idea about carbon sequestration.   

       Welcome to the HB, dataE. On the topics for CO2 sequestration and alternative use of fossil fuels there is a lot of good stuff to read.   

       /addendum: looks like Vernon's idea was to pour liquid nitrogen in the coal fires. Not the same.
bungston, Sep 02 2015

       WcW, I'm not certain about the carbon form or how it might be rendered harmless for the long term. I'm not thrilled with it but for a start it might be that only geologically stable structures would be targets for this type of process. At best we might be better than the status quo by eliminating processes that produce additional waste. At worst we might only be kicking the can...
dataloss, Sep 02 2015

       I like the idea (quite out of the box), but there is another serious flaw that hasn't been mentioned: heat rejection. Normally power is produced from coal using a heat engine. That requires a cold side to work. I don't think there would be enough thermal mass in the surrounding soil to act as the cold side.   

       You could of course pump cold water down to it...
scad mientist, Sep 03 2015

       carbon/carbon-monoxide fuel cell maybe ?
FlyingToaster, Sep 03 2015

       For the cooling process I wondered about how ridiculus it might be to use liquid oxygen since that would help reduce the volume of intake air and thereby minimize the volume of exhaust gas that needs to be sequestered. What advantage we might have gained by reducing surface facilities might be lost in the production and management of the cryogenic system.   

       So if we throw out the pure oxygen and cryogenics than we can have a leaner burn which will result in a greater production of carbon monoxide ... still ugly stuff...
dataloss, Sep 03 2015

       Just point the thing downwards. At some point you'll get geothermal energy.
MaxwellBuchanan, Sep 03 2015

       It looks like liquid oxygen use is viable and is currently in use at some power plants. So we are back to a TBM configuration with a cutting head, liquid oxygen fed furnace, generator, heat rejected by the liquid oxygen (let's go full rocket science on this). From some of the estimates on transportation cost the system should provide a 10-50% advantage.   

       The link also suggest another option that might be considered that would force CO2 into a coal seam to release methane and then burn that methane with liquid oxygen to run the furnace/generator... wait then we feed the CO2 back to coal seam... is that gonna work?
dataloss, Sep 03 2015

       Fracking for coal...
MaxwellBuchanan, Sep 03 2015

       Cooling with liquid oxygen won't net you any energy. The energy produced by a heat engine comes from taking something hot and something cold and ending with a more uniform temperature between the two. It will take just as much energy to produce the cold liquid oxygen as will be gained by the heat engine having this cold source.   

       The quick search I did seems to indicate that liquid Oxygen is used in power plants as a way of storing energy at non-peak times (producing liquid O2), and boosting output at peak times (burning with O2 instead of air and using stored thermal energy).   

       Maybe a better answer for your idea would be a direct carbon fuel which I didn't even know existed until today.
scad mientist, Sep 03 2015

       Agree, the liquid oxygen is a Rube Goldberg step to reduce the volume of air being pumped down to the furnace so to produce a much hotter burn with lower waste volume and denser CO2 that could more readily be scrubbed and sequestered in the capped geological structure that the TBM is operating within. Since we are going through the trouble of using pure oxygen and we need a coolant why not take advantage of the incoming LOX flow. The use of LOX is a net energy loss step but overall it will produce a much more efficient burn. That along with the complete removal of the high energy cost for coal transportation, coal processing, waste ash processing and transportation should provide a subsurface TBM with a significant net advantage.   

       Could you add the link for the direct carbon fuel.
dataloss, Sep 03 2015


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