hydrogen manegment

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Hydrogen management

Reners are facing the challenge of meeting

increasingly higher quality product speci-

cations to make clean fuels product, while

at the same time purchasing lower-quality

H2-decient crudes. As a result, H

2 requirements

have been steadily increasing and reneries are

nding that proper H2 management is increas-

ingly important to their long-term viability.

This article will describe the process KBC has

successfully used to eliminate H2 availability

constraints and prioritise H2 use in order to

improve protability.

Increasing refinery complexity and H2

requirementsReneries have various levels of complexities

and operating objectives. The simplest renery

type is the hydroskimming renery. Figure 1

show a typical hydroskimming renery congu-

ration. Hydroskimming reneries typically do

not need a H2 plant, as the H

2 demand can be

adequately met by the naphtha reformer.Margins are often low at hydroskimming rener-

ies unless there is a large marketing advantage,

usually based on location.

Rick Manner KBC Advanced Technologies

It is typically advantageous to maximise the

production of higher-value transportation fuels

instead of lower-value fuel oil products. As a

result, most protable reneries are either

moderately complex or highly complex facilities

that have cracking and conversion units. H2

requirements can vary greatly from one congu-

ration to the next.

Figure 2 shows a typical conguration for a

moderately complex renery, which employs an

FCC and a visbreaking unit to increase product value. The addition of a gas oil hydrotreater for

the FCC feed increases the renery H2 demand

beyond what the reformer alone can provide. A

small H2 plant is therefore also needed.

Figure 3 shows a complex carbon rejection

renery. A coker is added to convert fuel oil to

more valuable products. Light coker gas oil is

hydrotreated in the diesel hydrotreater and

heavy coker gas oil is hydrotreated in the gas oil

hydrotreater. Now, a medium-sized H2 plant is

required.Figure 4 shows a complex hydrocracking ren-

ery conguration. Substituting a hydrocracker

for the FCC unit increases H2 requirements to

www.digitalrefining.com/article/1000333 April 2012 1

Figure 1 Hydroskimming refinery configuration

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2 April 2012 www.digitalrefining.com/article/1000333

Figure 2 Moderately complex refinery

Figure 3 Complex carbon rejection refinery





vulnerable to upsets that could be mitigated if

connections between isolated systems are

established.

The primary goal of a H2 management study is

to identify the constraints imposed by the overallsystem and various H

2 subsystems, and nd

ways to remove these constraints to improve

overall renery protability. Typical solutions

can be as simple as rerouting streams to maxim-

ise high-margin units at the expense of others or

more complex and capital intensive, such as

building H2 recovery units, debottlenecking

steam-methane reformers or installing additional

compression to provide additional exibility and

increase prots.


H2 management study tools

Renery H2 systems can be extremely complex.

As a result, it may be very difcult to evaluate all

of the possible H2 management opportunities

without the aid of specialised tools. KBC hasdeveloped two software products that are used in

our H2 management studies. The combination of

KBC’s HydrogenPinch and Petro-SIM software

is extremely effective in evaluating the value of

rerouting streams and/or removing constraints

in order to improve overall renery protability.

HydrogenPinch is KBC’s proprietary software

designed primarily to identify H2 system oppor-

tunities such as the optimal routing of H2

streams at a renery. This software evaluates the

Figure 5 Addition of residua hydrocracking

Figure 6 Study methodology diagram





example of this could be as simple as preferen-

tially sending lower-purity H2 streams to process

units like kerosene hydrotreaters that do not

require high purity to more complex opportuni-

ties to connect distinct separated H2 systems

based on purity, pressure or geography.

It is important to continue evaluating rerout-

ing options even after a more protable option is

found. An option is not necessarily the most

protable option just because it is an improve-

ment over the base case.

Recovering H2 from fuel gas is often a very

attractive recommendation from H2 management

studies. The most attractive technologies that

reneries typically use for this purpose are:• Pressure Swing Adsorption

• Membrane H2 recovery

• Feeding H2-rich streams to SMR H

2 plants to

recover H2.

Pressure Swing Adsorption

Pressure Swing adsorption (PSA) H2 purication

units produce a 99.9%+ purity H2 product typi-

cally from process streams containing 60-80%

H2 that would otherwise go into the renery fuel

gas system. The process uses proprietary adsorb-ents that capture essentially all non-H

2

compounds at system pressure (typically 250-

300 psig) and desorbs the adsorbed material to

fuel gas at very low pressures (typically 5 psig).

A PSA usually consists of 4-12 beds that alter-

nate between adsorption, depressuring and

purging to fuel. The pressuring and depressuring

sequences are optimised to minimise the amount

of H2 sent to fuel. Typical H

2 recoveries vary

between 80-90%.

PSA is a proven H2 recovery option

that is the clear choice when 99.9%+

H2 purity is required. The major

drawback to PSA H2 recovery units

is the cost of compressing the fuel

gas by-product. It is the clear

preferred choice in situations where

there is a large fuel gas user that can

accommodate low-pressure fuel gas

like a Steam Methane Reforming

(SMR) H2 plant furnace.

UOP and Linde are the two

primary suppliers of PSA technology.

Both licensors provide excellent

units that work well, although they

do not always achieve design H2

recovery. ExxonMobil and QuestAir have a

lower-cost version of the process called Rapid

Cycle PSA (RCPSA) that uses a rotating cylinder

instead of multiple beds and produces a lower-purity product at lower recoveries. There is a

niche application of this technology that allows

reners to improve recycle H2 purity at diesel

hydrotreating units that may make it a good

choice for some reneries.

Membrane H2 recovery

Membrane H2 recovery units operate based on

the difference in permeability between H2 and

the contaminants present in the H2 recovery

unit feed. The H2 permeates through amembrane and is recovered at a pressure that

is typically one-third of the inlet pressure. The

non-permeate gas contains about 10-15% of the

H2, and most of the non-H

2, and is available at

high enough pressure for fuel gas. The compo-

sition of permeate and non-permeate along the

membrane was calculated based on typical rela-

tive permeabilities of H2 and non-H

2

components. Based on these calculations, a

curve describing H2 recovery as a function of

permeates purity for three different feed puri-ties. Based on the location of the design point

near the bend in each curve, an operating curve

was developed to allow for estimation of H2

recovery and H2 purity at various feed qualities.

Figure 7 illustrates this relationship. Air

Products (PRISM), Air Liquide (Medal) and

UOP (PolySep) are major vendors of membrane

H2 recovery technology. A typical performance

curve for a membrane H2 recovery unit is shown

in Figure 7.


Figure 7 Typical performance curve of a membrane H2 recovery unit





Membrane H2 recovery units

produce a lower-pressure H2

product and a high-pressure fuel

gas product. Membrane units are

a good choice for improving the

purity of high-pressure purge gas

off of a hydrotreater or hydroc-

racker and recycling the lower

pressure H2 to the make-up

compressor. If make-up compres-

sor capacity is not available, it is

more difcult to justify a

membrane H2 recovery unit

instead of a PSA.

Membrane H2 recovery is a

proven technology that has been

in continuous use in many ren-

eries for over 25 years. However,

membrane units cannot tolerate any liquids in

contact with the membranes and many renerieshave experienced this problem. In addition,

membrane units require some attention to start-

up or shutdown modules as conditions change as

run length progresses. They are not difcult to

operate, but the learning curve is much more

difcult than with a PSA

Route H2-rich feed to an SMR H

2 plant

H2 plants are excellent H

2 recovery units. H

2 in

H2 plant feeds typically appears as product at

very high recoveries and causes little or noincrease in red duty. Reners that have hydrau-

lic capacity should consider using their H2 plants

as H2 recovery units. Debottlenecking H

2 plants

is another option available that may be relatively

low cost for many H2 plants.

Cryogenic H2 recovery

Cryogenic H2 recovery is a proven technology

that requires low temperatures to separate H2

from light hydrocarbons in a cold box. A simpli-

ed diagram of a cryogenic H2 recovery unit isshown in Figure 8.

H2 recoveries are typically 95% and H

2 product

purities are 97% or higher at a typical cryogenic

H2 recovery unit. However, cryogenic H

2 recov -

ery units are very expensive and do not scale

down easily. As a result, they are usually only

economical if there is an incentive to recover the

light hydrocarbons in the feed as discreet

streams and the plant is very large (>100

MMSCFD).

Recontacting to improve H2 purity

Recontacting H2-rich streams with lean oils that

can absorb light hydrocarbon may be an inex-

pensive way to improve H2 purity at some units.

Recontacting is frequently used by UOP in some

of their Platformer designs to recover LPG and

improve H2 purity. It is less common in

hydrotreaters, although it can be just as effective.

Recycling liquid from a low-pressure ash drum

or a product stripper/fractionator back to the

high-pressure separator to sponge out heavier

hydrocarbons can be an effective way to improve

recycle gas purity. However, it is usually onlyeconomical if the hydrotreater was originally

designed for a much higher feed rate or the ash

drums are signicantly oversized.

Summary and conclusions As reneries have got more complex, the need

for H2 has increased, and understanding the

details of the renery H2 system has become

increasingly important. A H2 management study

can help identify opportunities, evaluate and

implement an action plan that will lead toincreased renery protability and exibility.

A proper H2 management study will give the

rener a complete understanding of the H2

system and identify valuable opportunities to

improve system performance. Options for

improvement include identifying the cost and

value of H2 at each producer or consumer and

rerouting H2-rich streams, exploring H

2 recovery

schemes, H2 plant debottlenecking options and

additional operational changes that can be easily

www.digitalrefining.com/article/1000333 April 2012 7

Figure 8 Cryogenic H2 recovery unit





implemented to help maximise renery

protability.

Petro-SIM is a trademark of KBC Advanced Technologies plc, and

it is registered in various territories.

Rapid Cycle PSA (RCPSA) is a trademark of Exxon Mobil Corporation

and QuestAir and it is registered in various territories.

PRISM is a trademark f Air Products and it is registered in various

territories.Medal is a trademark of Air Liquide and it is registered in various

territories.

PolySep is a trademark of UOP and it is registered in various

territories.


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