Re: Hydrogen as Coal replacement, NOx emissions.

On Dec 21, 6:27 am, jgra...@xxxxxx wrote:
Willie.Moo...@xxxxxxxxx writes:
...The success of that project triggers several power plant projects that
will switch from coal to hydrogen which I have recently negotiated.
This hydrogen is delivered from old mine sites by hydrogen gas
pipeline, along high tension wire rights of way, Do enough coal
fired power plants in a region,

Does burning hydrogen (in air) in a converted coal power plant produce
NOx emissions?

It can.

If so, and if it were desireable to reduce the NOx,
how could that be accomplished?

The formation of "thermal NOx" increases with increases in the
concentrations (amounts per unit
volume) of nitrogen, oxygen, and the combustion temperature. At
combustion temperatures below
2,370F, smaller concentrations of NOx are formed, and below 1400F
almost no NOx is formed.
The methods for the reduction of NOx formation are all based on
controlling the temperature
and/or by limiting one or more of the concentrations of oxygen,
nitrogen, or the fuel.

1. Less Excess Air

Air in excess of that required to completely oxidize the fuel has been
shown to correlate with
the amount of NOx formed. Limiting the net excess air flow to under 2%
limits the amount
of excess oxygen available for the formation of NOx

2. Air Staging

To effect air staging, the air is divided into two streams. In the
first stream, fuel is mixed with
an insufficient amount of air for complete combustion. The second air
stream is injected
downstream from the flame and results in a slight excess of air. This
technique is used to keep
the temperature relatively low as well as the oxygen concentration in
the primary combustion
area. High efficiencies have been reported with the use of this
technology.

3. Over Fire Air

This is another technique for reducing the combustion temperature by
staging the main
combustion zone such that the combustion temperature is lowered
thereby lowering the
formation of NOx. In this approach, the primary combustion is carried
out with a fuel-rich
mixture. The lack of oxygen needed for complete combustion holds down
the combustion rate
which in turn limits the combustion temperature. After the stages of
combustion have been
completed, the remainder of the fuel is oxidized in over fire air. In
this process, some excess
of air is used

4. Fuel Reburning

When cooled combustion gas and additional fuel are recirculated, some
of the heat of
combustion is absorbed by the cooled combustion gas thereby lowering
the temperature and
the NOx production. Also, when the cooled combustion gas and fuel are
added as a secondary
combustion stage, the oxygen in the NOx tends to oxidize the fuel
producing molecular
nitrogen (N2) and oxygen (O2). Burning of the remaining fuel is
completed in a later stage
using either combustion air nozzles or over fire air. This technique
has been demonstrated to
be effective with residence times from 0.2 seconds up to 1.2 seconds.
Reductions of NOx up
to 76% have been achieved by this technique

5. Low NOx Burners

In a low NOx burner, a stable flame is provided over several different
zones. As an
example, the first zone can be primary combustion, and the second may
be fuel reburning
in which fuel is added to chemically reduce the NOx to molecular
nitrogen (N2) and
oxygen (O2). The third zone may consist of the final combustion which
is carried out with low
excess air to limit the temperature. Many variations of the above LNB
for the reduction of
NOx exist.1,4 The LNB control technology has the largest experience
base of any technology
in the United States. Over the last decade, several generations of low
NOx burners have
evolved; see for example Bab*** Borsig Power, DB Riley.7 The low NOx
burners (LNB)
have achieved up to 80%*1reduction of NOx.

Add an oxygen pipeline in the same right-of-way,
and burn the H2 in O2 instead of in air,
instead of just venting the O2?

Depends on the logistics of doing this. This is possible in a
regenerative fuel cell type application for example, but would not be
feasible in other applications.


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