[ExI] syngas

[Keith Henson]

Interaction between SolarSyngas and the Power Grid

The engineering numbers in this discussion are not exact, but are close
enough for quantitative analysis.

Fully built out, SolarSyngas, which is making syngas (carbon monoxide and
hydrogen) from municipal solid waste (MSW) and excess renewable power, is
an enormous project. Los Angeles, for example, makes around 75,000 tons of
MSW per day. It would take 30 of the currently analyzed 2500 tons per day
gasifiers to cope with this flow. Each of the gasifiers of current design
would use 160 MW of renewable power. The total for LA would be 5.8 GW.
That’s a lot of power. The Pacific Intertie is only 3 GW. On the other
hand, California is planning 5 GW of additional solar PV over the canals so
perhaps this is not entirely unreasonable.

The gasifiers would constitute a controllable load able to absorb all
electrical energy--particularly renewable energy in excess of current
demand.
Each gasifier would make over 100 tons of syngas per hour. While this
sounds like a lot, municipal gas companies made similar amounts from coal
for over a hundred years.

The energy content of the gas is ~12.2 MWh for 4 MWh input. The gas burned
in a 60% efficient combined cycle turbine would recover ~7.2 MWh of power.
Making more power than the gasification uses means the gasifiers can run 24
hours a day while also generating power. As a reality check on this, there
were small gasifiers that used plasma torches for heating. They fed the
off-gases to 25% efficient reciprocating engines that supplied most, if not
all, the energy needed to run the plasma torches. (from memory 20 years
ago, so check on this)

Syngas made during the day from renewable energy (mostly solar) would be
stored and burned for power after the sun goes down, in place of natural
gas.

Syngas storage for daily to monthly use or longer can probably be done
using empty gas fields, though leaks of carbon monoxide are a concern.
Hydrogen leaks are also difficult to contain. If this becomes a major
problem, syngas can be converted with some energy loss to methane for
long-duration storage. The Great Plains Synfuel plant converts 12,000 tons
of coal per day into pipeline quality natural gas. I.e., this is a well
understood industrial process.

Taken as a whole, a built-out SolarSyngas project can be considered a very
high capacity, long-storage-duration battery.
Besides MSW, gasifiers can be fed with biomass. The gasifiers depend on a
pool of liquid iron, so those fed mostly on biomass will require some
additional iron or possibly iron oxide in the feed.

The other option is to make liquid fuels from the syngas. Replacing a
serious fraction of oil use with synthetic fuels will likely require a high
flow of biomass. There are uses for hydrocarbon fuels that are expensive or
difficult to electrify: long-distance aviation, farming, some long-
distance railroads, and perhaps trucking over mountains.

Cleaned syngas, perhaps with extra electrolytic hydrogen, can be processed
into jet fuel or diesel. There is a plant in Qatar that makes 34,000 bbl of
diesel per day out of syngas, so this is a process understood at scale.

Humans use an enormous amount of energy. Replacing the carbon part of that
with sustainable sources is an enormous project

Keith
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