Hydrogen Recovery by Pressure Swing Adsorption 2

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Contents.

3 Introduction

4 The process

5 The PSA sequence

6 Scope of work

7 The advantages

8 Contact 3

Introduction.

The experience. The use of the Pressure Swing Adsorption (PSA) process has seen tremendous growth during the last decades mainly due to its simplicity and low operating costs. Major applications have been the recovery of high purity hydrogen, methane and carbon dioxide as well as the generation of nitrogen and oxygen. In addition, it has gained significance for the bulk removal of carbon dioxide from direct reduction top-gases.

Linde as the world leader in adsorption technology has designed and supplied more than 500 PSA plants – including the world‘s largest units and units with highest availability.

The Linde hydrogen PSA units Capacities range from a few hundred Nm³/h to As a second group of users in the petrochemical The well proven Linde high performance PSA large scale plants with more than 400,000 Nm³/h. industry has a demand for hydrogen for its units are designed for the recovery and purifi- The hydrogen product meets every purity re- methanol and ammonia synthesis, MTBE pro- cation of pure hydrogen from different hydrogen quirement up to 99.9999 mol-% and is achieved cesses, etc. -rich streams, such as synthesis gases from at highest recovery rates. steam reforming process, partial oxidation or Linde‘s PSA systems have proven to be success- gasification, as well as from various off-gases Main hydrogen consumers are refineries re- ful in cases where performance, flexibility, avail- in refineries or petrochemical processes, e.g. quiring this valuable gas for example for their ability and reliability are the determining factors. ethylene off-gas, coke oven gas, methanol and cracking, dearomatization or desulphurization High quality and easy accessibility to all compo- ammonia purge gas. processes. nents minimize and facilitate maintenance to the maximum extent. 4

The process.

Separation by adsorption Adsorption and regeneration The Pressure Swing Adsorption (PSA) technology The PSA process works at basically constant Adsorption is carried out at high pressure (and is based on a physical binding of gas molecules temperature and uses the effect of alternating hence high respective partial pressure) typically to adsorbent material. The respective force act- pressure and partial pressure to perform adsorp- in the range of 10 to 40 bar until the equilibrium ing between the gas molecules and the adsorb- tion and desorption. Since heating or cooling is loading is reached. At this point in time, no ent material depends on the gas component, not required, short cycles within the range of further adsorption capacity is available and the type of adsorbent material, partial pressure of minutes are achieved. The PSA process conse- adsorbent material must be regenerated. This the gas component and operating temperature. quently allows the economical removal of large regeneration is done by lowering the pressure A qualitative ranking of the adsorption forces is amounts of impurities. to slightly above atmospheric pressure resulting shown in the figure below. in a respective decrease in equilibrium loading. The figure on page 5 illustrates the pressure As a result, the impurities on the adsorbent The separation effect is based on differences in swing adsorption process. It shows the adsorp- material are desorbed and the adsorbent material binding forces to the adsorbent material. Highly tion isotherms describing the relation between is regenerated. The amount of impurities re- volatile components with low polarity, such as partial pressure of a component and its equili- moved from a gas stream within one cycle hydrogen, are practically non-adsorbable as brium loading on the adsorbent material for a corresponds to the difference of adsorption to opposed to molecules as N2, CO, CO2, hydrocar- given temperature. desorption loading. bons and water vapour. Consequently, these impurities can be adsorbed from a hydrogen- After termination of regeneration, pressure is containing stream and high purity hydrogen is increased back to adsorption pressure level and recovered. the process starts again from the beginning.

Qualitative ranking of adsorption forces Pressure swing adsorption plant in Leuna, Germany

Hydrogen weak

Oxygen Argon

Nitrogen

Carbon monoxide Methane

Carbon dioxide

Ethane Ethylene Propane Butane Propylene Ammonia Hydrogen sulfide Mercaptanes BTX

Water strong 5

Adsorption isotherms

Adsorption loading

0°C

30°C

Differential loading Differential 50°C

Desorption loading

200°C

PD Partial pressure PA Desorption pressure Adsorption pressure

Adsorption and regeneration by pressure swing The PSA sequence.

A PSA plant consists basically of the adsorber material. Highly pure hydrogen exits the adsor- total number of adsorbers and the process con- vessels containing the adsorbent material, tail ber vessel at top. After a defined time, the ad- ditions, one to four of these so-called pressure gas drum(s), valve skid(s) with interconnecting sorption phase of this vessel stops and regen- equalization steps are performed. Each addi- piping, control valves and instrumentation and eration starts. Another adsorber takes over the tional pressure equalization step minimizes a control system for control of the unit. task of adsorption to ensure continuous hydro- hydrogen losses and increases the hydrogen The pressure swing adsorption process has four gen supply. recovery rate. basic process steps: – Adsorption Regeneration Provide purge (step PP) – Depressurization The regeneration phase consists of basically This is the final depressurization step in co- – Regeneration five consecutive steps: current direction providing pure hydrogen to – Repressurization – Pressure equalization purge or regenerate another adsorber. – Provide purge To provide continuous hydrogen supply, mini- – Dump Dump (step D) mum 4 adsorber vessels are required. The figure – Purging At a certain point of time, the remaining pres- on page 6 shows the combination of the sequen- – Repressurization sure must be released in counter-current direc- ces of four adsorber vessels as a pressure-time- tion to prevent break-through of impurities at diagram. The steps are combined so as to minimize hydro- the top of the adsorber. This is the first step of gen losses and consequently to maximize the the regeneration phase when desorbed impuri- Adsorption hydrogen recovery rate of the PSA system. ties leave the adsorber at the bottom and flow Adsorption of impurities is carried out at high to the tail gas system of the PSA plant. pressure being determined by the pressure of Pressure equalization (step E1) the feed gas. The feed gas flows through the Depressurization starts in the co-current direc- adsorber vessels in an upward direction. Impuri- tion from bottom to top. The hydrogen still stored ties such as water, heavy hydrocarbons, light in the void space of the adsorbent material is hydrocarbons, CO2, CO and nitrogen are selec- used to pressurize another adsorber having just tively adsorbed on the surface of the adsorbent terminated its regeneration. Depending on the 6

Scope of work.

Purging (regeneration) The typical scope of supply Final desorption and regeneration is performed of Linde‘s PSA units includes: at the lowest pressure of the PSA sequence. – Prefabricated valve skid Highly pure hydrogen obtained from an adsorber – Adsorber vessels in the provide purge step, is used to purge the – Specially selected adsorbent material desorbed impurities into the tail gas system. – Tail gas drum The residual loading on the adsorbent material is – Process control system reduced to a minimum to achieve high efficiency of the PSA cycle. The scope can be altered to best suit client‘s needs. Based on the customer‘s requirements, Repressurization (steps R1/R0) feed gas compressor or tail gas compressor Before restarting adsorption, the regenerated systems can be offered through Linde as a adsorber must be pressurized again. This is integrated PSA solution. accomplished in the pressure equalization step by using pure hydrogen from adsorbers presently under depressurization. Since final adsorption pressure cannot be reached with pressure equalization steps, repressurization to adsorption pressure is carried out with a split stream from the hydrogen product line. Having reached the required pressure level PSA valve skid again, this regenerated adsorber takes over the task of adsorption from another vessel having just terminated its adsorption phase. Pressure time diagram

Adsorber A

Adsorption E1 R0 Pressure

PP R1 D Regeneration Adsorber B

R0 Adsorption E1

R1 PP D Regeneration Adsorber C

R0 Adsorption

D PP Regeneration R1 Adsorber D

R0 Adsorption

PP D Regeneration R1

Time 7

Two pressure swing adsorption units in Canada The advantages.

The Linde high performance PSA units provide remarkable advantages such as:

Linde‘s expertise in adsorption technology Availability Modular design and prefabricated equipment Based on customer‘s requirements, the Linde The Linde PSA systems are characterized by an Linde‘s high performance PSA systems are pre- PSA specialists will select the optimum PSA outstanding availability of hydrogen supply. fabricated to a maximum extent. The valve skids system for the specific purification task in terms With its special features such as operation with containing switching and control valves, instru- of optimum ratio between plant performance reduced number of adsorbers, adsorber group mentation and interconnecting piping are com- and investment cost. isolation and redundant control system, Linde‘s pletely prefabricated, preassembled and tested PSA units achieve virtually 100% on-stream prior to delivery. This design philosophy reduces Quality performance and availability. time and costs for erection and commissioning The high switching cycles of PSA units require on site to and absolute minimum. special equipment distinguished by a high de- Flexibility gree of durability. Linde only applies qualified Excellent flexibility to match actual client‘s Easy maintenance components, which meet these demands per- needs are achieved with Linde‘s PSA systems Maintenance is limited to easy and quick rou- fectly and which are proven during many years as they are capable of providing a high degree tine actions which can be carried out by the of experience. of flexibility to cope with feed gas conditions operators on site. Highest attention is given to and varying hydrogen demand. a proper accessibility of all valves and instru- Reliability ments inside the valve skid. Assistance from The use of selected and suitable components Linde is hence normally not required but is implies the high reliability of Linde‘s PSA sys- certainly available at any time convenient to tems. Especially high performance switching client. valves are used in Linde‘s PSA process. → → → → → Plant engineering at aglance Core competencies +281.717-9090 Phone: team: plant adsorption our with touch in Get Discover how we can contribute to your success at www. leamericas.com world. the in –anywhere needs your fit best that services and solutions the to deliver us on rely always You can conditions. all under cost-effectively and reliably operate that solutions plant develop specialists our builds, to customised standardised from to world-scale, small- from Arctic, to the desert the From worldwide. 100 countries than more in working employees by our passion with delivered and partners strategic our with collaboration close in –designed plants pilot and labs centres, R&D tech high- at our equipment and technologies process innovative to develop us inspires connection This needs. your to meet you with closely collaborate and carefully We listen customers. our with relationships business lasting trusted, value we At Linde, processing. metal and to chemical refining and extraction gas natural oil, crude –from industries multiple across customers ofour success the in role indispensable an plays know-how technology and process proven Our facilities. industrial ofturnkey construction and management project design, the in step every cover and plants 4,000 than more delivered have we globe, the Across business. engineering plant international the in player aleading is Division Engineering Linde’s Collaborate. Innovate. Deliver. → → → → → → → → → → → Ad Hy Pet LN Air Fu Car Cr yogenic plants yogenic rnaces, fired heaters, incinerators G and natural gas processing plants drogen and synthesis gas plants sorption plants separation plants bon capture and utiliz rochemical plants , e-mail: sales , e-mail: ation plants americas.com @le → → → → → → → → → Component manufacturing → → → → → → → → → Sp Wa Ai Liq Cr Cr Pl Co Co ate-fin heat exchangers z r-heated vapori yogenic storage tanks yogenic columns iral-welded aluminium pipes il-wound heat exchangers heat il-wound ld boxes and modules uefied helium and tanks containers z vapori bath ter ers ers Services → → → → → → → → → → → → → → and spare part inventory part spare and and immediate repairs Op Ex Lo Op Sp Pl Re ant relocations ng-term service contracts service ng-term pert reviews for plants, operations operations plants, for reviews pert are parts vamps and plant modifications erator training troubleshooting erational support,

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