Dew point of gas-hydrogen blends

[siricosm]

With all this talk about potentially switching from gas to hydrogen or even blending some hydrogen into the gas, does anyone know how this affects the dew point of the products of combustion? With natural gas I think it starts to condense around 57C or so, so the return temperature needs to be under that to get significant condensing in a modern boiler. If the gas was blended with say 10% hydrogen, does it change that temperature? Actually it would be nice to see a chart going from 0% 10%, 20% ... 100% hydrogen. Has anyone seen such a chart?

 

[Matt0029]

This would be interesting to know.

 

[ShaunCorbs]

Will be the same as natural gas or winthin a degree of two

 

[SJB060685]

Mains gas is CH4, 1 part carbon and 4 parts hydrogen. The higher the hydrogen content within a fuel the more water vapour is produced as a by product. This in turn leads to a higher partial pressure of water vapour in the medium (this case the flue gases) which increases its dew point temperature.
Mains gas is as you say starts to condense at about 57°c and condenses considerably more the lower the return temperature can be. Oil on the other hand has less hydrogen in it and as a result requires a temperature closer to 47°c to start condensing.

 

[gmartine]

What I was astonished to read was that the CO2 emissions saving was less than 10% running a gas blend which is better than nothing but still, hardly planet saving considering the push. Yet modern building and existing insulation standards are relatively Sod poor.

 

[siricosm]

So although it may only change a small amount, it will be in the right direction as far as condensation is concerned, as the more hydrogen there is, the higher the return temperature can be, which is good.

Still would be nice to see a table, that gives the temperature for various blends up to pure hydrogen. I can't seem to find one.

 

[oz-plumber]

You probably never will!

As far as I am concerned, the only thing that is going to make major changes to the state of the environment is Government Legislation.

Governments will not make Legislation's that will impact all its Citizens financially to a substantial amount.

Imagine a Government that declares we are going to Greener Energy.
It will only amount to an extra 20% across all your energy bills, including vehicle registration and fuel prices.

I live in Melbourne.
The amount of money you pay for a solar hot water system will take about 8 years to recoup, over having a non solar system installed.
Where the benefit in that?

 

[Ric2013]

I live in Melbourne.
The amount of money you pay for a solar hot water system will take about 8 years to recoup, over having a non solar system installed.
Where the benefit in that?

With today's interest rates, 8 years is not bad, really, so may be worth it, in Melbourne. The solar installation also makes your boiler last longer and should itself last some considerable time. Of course, if the hot water system becomes a status symbol, then the cost is irrelevant. After all, how long does double-glazing really take to pay for itself vs draughtproofing existing single-glazed windows in the UK, and how many houses still have single-glazing?

It seems the costs of mitigation of climate change will be much lower than the adaptation costs. It has been suggested that people who can afford it will accept extra costs happily enough. The problem is that systemic change is required and it has been suggested that people will accept cost, provided they don't have to change their lifestyle - which would be required if we are to ditch the current relentless pursuit of continuous economic growth.

The trouble is, the powers that be have an interest in the current economic system and they do a very good job of influencing mainstream thought. Governments will tend to lag behind ideas whose time has come.

 

[gmartine]

Home radiators will have to be 10 degrees cooler for Britain to reach climate targets

The Government has said it wants hundreds of thousands of heat pumps to replace gas boilers

www.telegraph.co.uk

 

[Chuck]

Has anyone seen such a chart?

Here's a quick calculation that assumes 10% excess air and uses the Antoine formula to calculate SVP for water as a function of temperature.

 

[siricosm]

Wow, that is a lot by the time you get to pure hydrogen, around 25C. This means that boiler running on pure hydrogen will not really need over sized rads to be condensing most of the time.

 

[Chuck]

Wow, that is a lot by the time you get to pure hydrogen, around 25C. This means that boiler running on pure hydrogen will not really need over sized rads to be condensing most of the time.

I think you must mean 15°C. Keep in mind that if the return temperature is at the dew point the amount of condensation will be negligible. It needs to be significantly lower to actually have a significant impact.

For example, at a dew point of 57°C the partial pressure of H2O in the combustion products will be 131 mmHg. A return temperature of 45°C will reduce the H2O SVP to 72 mmHg, which means that only about 45% of the H2O will be condensed.

According to my calculation, a boiler that runs on pure H2 with lambda = 1.1 will have a pp(H2O) = 240 mmHg. A return temperature of 55°C, which corresponds to SVP of 118 mmHg, will allow 50% of the H2O to condense.

 

[SJB060685]

I think you must mean 15°C. Keep in mind that if the return temperature is at the dew point the amount of condensation will be negligible. It needs to be significantly lower to actually have a significant impact.

For example, at a dew point of 57°C the partial pressure of H2O in the combustion products will be 131 mmHg. A return temperature of 45°C will reduce the H2O SVP to 72 mmHg, which means that only about 45% of the H20 will be condensed.

According to my calculation, a boiler that runs on pure H2 with lambda = 1.1 will have a pp(H2O) = 240 mmHg. A return temperature of 55°C, which corresponds to SVP of 118 mmHg, will allow 50% of the H2O to condense.

I'm liking your maths and clearly clarifies what I said above in my comment.

 

[siricosm]

Haha, yes, 15C.