How to calculate BTU/hr to heat water?

Are you trying to get steam or do you just need hot water? if you just need hot water, heating to 100 deg C may be extreme...wouldnt mind knowing the application

A btu is the energy it takes to raise 1 lb of water by 1 degree Fahrenheit.

1L water = 2.2 lb

Assuming you use the whole 100 L every hr then you use 220 lb of water per hr. If you raise the T by 60 deg C then you raise it 140 F so i think youd use 30800 btu/hr...

Dont know if this answers your question completely, but i think it should help. Use Natural Gas wherever possible especially in boilers, so much more efficient!

PS get an account on here so we can know if it is you responding or not..

Thank you. I need a safety valve to cut off the gas flow when tilting the drum - no electricity around.

can't help you with that, i am no where close to being a mech guy, i only know this because i have been working with boiler efficiencies lately...

That means you got no burner controls and doing everything manually also because there is no electricity. So before you tilt the drum just manually shutt off the gas valve.

Achilles answered your question #1.

Since you have a gas burner and assuming you are controlling it with a temperature controller set at 100°C. " I need a safety 'tilting valve to cut off the gas flow when tilting the drum?". Use a Limit Switch on the side of the drum with an additional main Solenoid Valve to shut off the burner the moment you move the drum. This Solenoid will be only for this safe-tilting protection and to come on when the drum reaches its original position. The burner FSG system will be working as is.