Q & A > Question Details
if we want to reduce the Hydrogen purity in DIESEL HYDROTREATER the current H2 purity is 99.99 fro PSA Unit now we want to take from other plant (Rheniformer units),During hydrogen plant turnaround, PSA’s are not in operation and only the off gas from Rheniformer units, low purity hydrogen, is available. This make-up gas can be used as hydrogen for the DHT to keep it running for the duration of the whole hydrogen plant outage.
the hydrogen from PSA :
HYDROGEN ------> 99.99
C1------> 0.1
CO + CO2 -----> 20 MAX
H2S ----> ZERO
HCL < 1
***** new hydrogen make-up with a reduced purity, coming from Rheniformer units
H2 87.5
C1 5.8
C2 3.6
C3 1.6
C4 0.4
C5+ 1.1
- what is the side effect of low purity for all the plants, recycle compressor, make up compressor and the load in addition the make up it is suitable for for such low purity?
What is the impact on
-Reaction section
-Product quality
-Recycle compressor?

22/04/2012 A: Satish Angadi, Haldor topsoe, satish.angadi@gmail.com
You did not mention whether unit has hot separator or not. This is important input.
If yes:
1) The recycle gas amperage will increase.
2) makeup gas flow, and power requirement will increase. Will be able to supply all the hydrogen required that depends on ''acfm"of MUG compressor capacity.
3) The catalyst will deactivate faster, faster than you think. You must consult catalyst supplier on this.
4) The product quality can be same, you may need to adjust Reactor temperatures.
5) The purge from Recycle gas KO drum can help you, but it depends on unit MUG compressor capacity.
If your unit has cold separator layout (no hot separator):
It (deactivation of catalyst) won't be as bad as above.
Your recycle gas purity can be higher than makeup gas purity. But above points will still hold good.
07/04/2012 A: Virendra Kapoor, Petroleum Refining Consultants, vkkapoor9@yahoo.com
It is easy to calculate hydrogen partial under the two situations. With the process correlations supplied by the catalyst vendor / process licencor, it is possible to estimate accurately the effects of the change on the product qualities such as HDS, Cetane improvement. Chloride level in the gas to HDSU / DHDTU is normally tolerable in the range about 3 or 4 ppmv from CRU
20/03/2012 A: Raghavendra Sangam, Libra Techcon Ltd., rsangam0504@yahoo.co.in
Such low purity hydrogen make-up in DHDT will reduce the conversion and reduce the unit capacity. For the same extent of hydrotreating, you may have to increase the make-up H2 flow rate to have the near design H2 partial presuure in the reactor beds.

(1) You may have to reduce the space velocity for the same conversion, that is, reduce the feed rate.

(2) RGC will work, however, with lower power consumption as the make-up gas now has higher MW. But increased requirement for the flow will off-set this.

(3) Olefins in the new make-up gas will consume some of the H2, in presence of the catalyst, for saturation thus leaving lesser hydrogen for removing S and N.

(4) Check for chlorides in the new make-up H2. Higher chlorides will form ammonium chloride in the reactor effluents which will precipitate at higher temperatures, probably in one of the feed-effluent exchangers. If you have water wash-injection upstraem of this exchanger, it would help. Probably you are not having this facility. Accumulated chlorides will eat away the exchanger. Check the MOC.

If the PSA outage is only for a very short period, you may try this Rheniformer off gas just to avoid the DHDT unit shut-down.