3 replies to this topic

[Fr3dd]

Hi everybody,

I have a little doubt and I know that there is a lot of people over here with very useful information and experience, so I'm writing again asking for help.

As I've described in other posts, I'm working in a Used lubricant oil recovery plant wich collects used lubricant oil wich are flashed, routed through a Thermal Deasphalting unit and hydrotreated.

This plant has a Fuel Gas Distribution Network, wich will be fed with Natural gas and some gases coming from the process. I've been asked to evaluate if it is feasible to collect a sour gas stream coming from the process which, in some operating cases, has a very high concentration of H2S. I have to consider if the "Dilution" effect coud mitigate the effects of high H2S concentrations, i've performed rough calculations and the H2S concentration in the product stream (fuel gas) is expected to oscilate between 0.4 % (mass) and 2.5% (mass).

I'm not feeling very confortable with a stream with this quantity of H2S going through my plant in a distribution network, however I wanted to ask you the following:Is there a limitation in the H2S content of fuel gas, to be used mainly in Fired heaters and boilers?

Thanks in advance.

[maartenB47]

Fr3dd,
from memory, your senses don't register anymore above 100 ppmv and 1000ppmv is lethal. So from a safety standpoint, your intended gas concentration is a nogo.
We used a maximum of 50 ppmv in fuelgas in our refinery.
Of course also the environmental effect of releasing SO2 and possible sulphur corrosion in stacks can play a role, but I don't have quantitative data on this.

[paulhorth]

Fr3dd,
To add to what Maarten says:
In my view there are at least three problems to consider with your proposed sour fuel gas system:

• Safety. I agree with Maarten's comment. I believe that at least, you will need to equip every worker with a H2S detector, and provide breathing apparatus sets around the plant which can be put on within a few seconds of an alarm.
• Materials. The piping and equipment willl need to be to NACE material specification.
• Emissions. You will need to check whether the SO2 from the fuel gas will exceed your company's emissions limits, both in tonnage terms and ground level concentrations.

In all of these problems, you should consider the MAXIMUM H2S content of the fuel gas, when the sweet gas supply is shut off for whatever reason and you fill the system with very high H2S gas.

Paul

[ankur2061]

Fr3dd,

Let me put across the official version of H2S exposure to humans according to Appendix-A of API RP 49 - Recommended Practice for Drilling and Well Servicing Operations involving Hydrogen Sulfide.

The American Conference of Governmental Industrial Hygienists (ACGIH) recommends a Threshold Limit Value (TLV) of 10 ppm (8-hour TWA) and a short term exposure limit (STEL) of 15 ppm averaged over 15 minutes.

You should simply avoid the mixing of the sour gas stream with the sweet natural gas stream. In case we are talking very large quantities of high H2S content gas then you should send them to a gas sweetening unit to reduce the H2S content and then blend it with the sweet natural gas in a proportion so as not to exceed 10 ppm in the mixed stream for burning it as fuel.

Other concerns that Paul has raised need to be addressed too, such as the corrosion of piping and equipment due to high H2S content.

Regards,
Ankur.