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Transport only the end product - Electricity
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
Using coal fires
No mechanism. [bungston, Sep 02 2015]
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.
||I dont 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.
||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.
||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
||What happens to the poor seal?
||I'm not sure, perhaps she was broke.
||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.
||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.
||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
||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 theres 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
||What form does that carbon take, post scrubbing, and how
much energy do we net?
||Now there's a idea, [dataloss]. Summer barbecuing season could yield a reasonable amount of electricity if we all had cogenerating barbecues.
||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
||Mining E TBM vs LongWallMining Conventional Coal
||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)
||--- -y- Surface rail line and rail cars/trucks
||-y- -y- Consider the building of a TBM is equal to
that of a LongWallMining machine
||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
||A hydroponic TBM, sweeeeeeet. Almost interstellar.
||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.
||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...
||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
||You could of course pump cold water down to it...
||carbon/carbon-monoxide fuel cell maybe ?
||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
||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
||Just point the thing downwards. At some point you'll
get geothermal energy.
||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
||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.
||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.