Perspectives: Process Puzzler

Process Puzzler: Hold Off on a Hydrogen Hike

Consider other options than increasing the feed of fresh hydrogen

*THIS MONTH’S PUZZLER* We’re planning to increase the capacity of a diesel hydrotreater unit by replacing part of the recycle hydrogen currently used with fresh hydrogen from an existing 1,200-psig system. The header begins as an 18-in., schedule-80 pipe. The control valves are each fed from a line right off the header.* Figure 1* (http://goo.gl/S801qN) shows what the header system looks like: the 1,600-ft line now handles a flow of 868 million standard cubic feet per day (MMSCFD) of hydrogen; the expansion will raise the total flow to 918 MMSCFD. One branch delivers 5 MMSCFD to isomerization. Another branch services a variety of hydrotreaters. It runs 2,500 ft and furnishes 200 MMSCFD to a hydrocracker, and then goes 3,100 ft where a common branch feeds two diesel hydrotreaters, which get 75 MMSCFD and 63 MMSCFD, respectively, and an ultra-low-sulfur diesel (ULSD) hydrotreater, which is fed 75 MMSCFD. After the diesel header, the line decreases in size to 12 in. and goes 2,700 ft to a kerosene hydrotreater fed 85 MMSCFD. It then continues 2,600 ft to a naphtha hydrotreater that gets 75 MMSCFD and to another header that delivers 140 MMSCFD to a gasoline hydrotreater and 150 MMSCFD to a fluid catalytic cracker (FCC) hydrotreater. The expansion will increase the hydrogen flow to the diesel hydrotreater 2 to 113 MMSCFD from 63; the % open for the control valve only will increase to 76% from 61%, so the project has been approved. The flows are all nominal-high values. A production engineer now is questioning the idea of increasing the fresh H2 output; he’s afraid it will put a strain on the system. What do you think?   *LOOK AT THE BIG PICTURE* Anytime you increase the system demand by 50 MMSCFD, i.e., 6%, with a pressure control valve (PCV) already at 72%, there will be trouble. Obviously, the compressor supplying the H2 and the control valve are sized together. With higher flow, head will decrease eventually. The rise to 79% open for the PCV probably is caused by a drop in the compressor head.

Read more

More from this perspective...

Title

Neutralization Requires Basic Rethink

Waste disposal system shouldn't be treated as an afterthought.

10/06/2011

May Process Puzzler: Quick fix needed!

Readers recommend solutions for a pump control problem in this month's Chemical Processing Process Puzzler.

04/24/2007

May Process Puzzler: Boost the reliability of a solvent supply pump

Readers suggest solutions to cavitation in this month's Process Puzzler.

05/25/2006

March Process Puzzler: Does removal approach offer a quicksilver lining?

Readers consider ways to clean mercury from scrubber blowdown in this month's Process Puzzler.

03/01/2007

Making sense of temperature sensing

Readers provide solutions to a thermowell problem in this month's Process Puzzler.

01/06/2006

Make The Right Opening Move

Readers suggest how to relate valve position to flow.

08/15/2012

Make Models Match

Readers explain how differences in pressure can arise.

08/09/2011

Know when the end is near

Chemical Processing's readers offer tips about how to determine resin-reaction end point.

01/02/2006

Knock Out Polymerization Process Problems

Tackling equipment and compatibility issues is crucial.

03/13/2012

Keep Oil Sampling Safe

Any sample cooler requires a pressure relief valve

02/11/2014

Keep Catalyst From Overheating

Readers react to a fouling problem in an exchanger.

08/25/2010

Kayo Another Compressor Catastrophe

Reciprocating unit requires multiple revisions.

01/20/2014

June Process Puzzler: Forestall furnace foibles

Readers suggest how to address a hard-running vaporizer in this month's Process Puzzler.

05/16/2007

July Process Puzzler: Prevent the burn-out of a mixer

Readers suggest quick solutions to a solid-liquid mixing problem in Chemical Processing's monthly Process Puzzler feature.

06/28/2006

July Process Puzzler: Blow away conveying system problems

Readers suggest how to improve the reliability of a crucial blower in this month's Process Puzzler.

07/06/2007

January Process Puzzler: Sticky valve

Readers offer ideas for the cause of a sticky valve in Chemical Processing's monthly Process Puzzler feature.

01/03/2007

Is an Expansion Joint Good For the Long Stretch?

Contributors suggest how to handle thermal and water issues.

05/19/2010

Heat Exchanger Puzzler: Make the Best of a Blunder

Readers suggest ways to get an incorrect exchanger to do the job.

05/04/2011

Get out of the Soup

Readers clarify a consistency complication.

12/02/2008

Get Rid Of Problems Not Just Off-Gas

A variety of factors may compromise performance of an oxidizer.

01/15/2013