Catalysis 2023 Issue

10,000

10.0

0.0 0.5 2.0 1.5 3.0 2.5 3.5 1.0 5.0 4.5 6.0 5.5 7.0 6.5 9.0 8.5 8.0 7.5 9.5

pH shift of 1.7 (pH of 6.3 when MDEA injection started)

9,000

DMDS ow rate

8,000

Water wash injection started

pH analyser online

6,000 7,000

5,000

MDEA ow rate

4,000

4.0

3,000

2,000 1,000

% HS

Hours

DMS ow rate , gpm

HS , % DMDS totaliser , gal

MDEA totaliser , gal

MDEA ow rate , gpm

Figure 2 LCO hydrocracker sulphiding and passivation data

as needed. Using data from the Reactor Resources system, the refiner stayed below their stack sulphur limit of 160 ppm during the start-up. At hour 17, the water wash system was started to pre- vent salt deposition in the process fluid cooling equip- ment (see Figure 2). Deposits of NH₄SH can occur in heat exchangers and fin fans if water wash is not commenced. These salts result from the reaction of ammonia (NH3) with H2S and are highly corrosive. An inline pH analyser system tracked the pH as it climbed from 4.5 to 6.3. MDEA injection of 7 gpm (1,590 LPH) was started at hour 21. Over the next nine hours, the pH gradu- ally increased by 1.7. A pH shift of 1.0 was used as an indi- cator that enough nitrogen was in the system to passivate the diesel selective cracking catalyst. As the pH passed 7.5, MDEA injection was throttled back to a maintenance dos- age of 0.5 gpm (114 LPH) and held constant for the next seven hours. Back to normal operation During the length of the start-up, the client was able to use data from the online H2S analyser to hold the H2S con- centration in a safe range between 0.6% and 1.5%. DMDS injection was halted at hour 33 since the gas concentration data indicated that the catalyst had stopped taking up addi- tional sulphur. A two-hour hold with a bed temperature of 610°F (321°C) was required to complete the formation of the active sulphide phase. At this point, the unit was ready for normal operation. After three days of straight-run feed, LCO was brought into the unit while temperatures were held until the reac- tor bed exotherms were observed to be stable. The refiner commented that the unit reached the projected yield on the fourth day after unit feed rates and feed mix were increased to normal conditions. In the past, the unit required five to seven days to line out with projected yields. With the ability to monitor the recycle gas concentra- tion and chemical injection processes in real-time, the

refiner was able to complete the sulphiding process by using only 105% of the stoichiometric DMDS requirement instead of 180% as seen in the previous sulphiding, a sav- ing of over €300,000 ($330,000) in sulphur chemical costs. Furthermore, issues resulting from over-injection, such as compressor trips and purging of excessively sour gas, were totally averted. The pH analyser system allowed the customer to reduce the quantity of MDEA required. Only 103% of the calculated stoichiometric nitrogen was injected vs the 150% ordered, an additional savings of almost €20,000 ($22,000). Efficient sulphiding and precise injection The proprietary SmartSkid DMDS Injection System, online gas analysers, and pH analyser system equip refiners with excellent control over hydrocracker start-ups. Refiners have found that real-time analysis of the recycle gas H2S and H2 concentration allows for a faster, more efficient sul- phiding of the catalyst while minimising the environmental issues resulting from excess purging of sour gas to the flare or fuel gas system. Also, precise measurement of the pH change equates to precise injection of MDEA, confi- dence that the cracking bed activity is thoroughly passiv- ated, and avoidance of problems related to excess injection of nitrogen compounds. Randy Alexander is a partner with Reactor Resources, LLC, in Alvin, Texas. He has over 25 years of experience with hydrotreating and hy- drogenation catalysts. At Reactor Resources, he is involved in market- ing and technical support for sulphur chemicals and injection services that are utilised to sulphide hydroprocessing catalysts. He holds a Bachelor’s degree in chemical engineering from the University of Texas and an MBA from the University of Houston. Paul Temme is Director, Technical Services with Reactor Resources. He has over 25 years of experience in the catalyst and catalyst sul- phiding industries. He has over four years of experience as Director of Technical Services and as a Sales Account Manager. He holds a BS degree in chemical engineering from the University of Massachusetts.

Catalysis 2023