Recovery and purification of hydrogen using PSA technology

Today's needs

Today, many processes have a requirement for a high quality hydrogen feed, in some cases to chemically react with other feedstocks to form new products and in other cases to provide a reducing atmosphere to prevent oxidation. Increasingly the need is driven by environmental concerns, most specifically in refineries worldwide that are aiming to reduce both sulphur and aromatics in their products.

The hydrogen required can either be produced by generating it, using a steam reforming or methanol cracking process, or recovering if from a hydrogen rich process stream by using the Pressure Swing Adsorption (PSA) process. Hydrogen rich process streams, readily available in refinery and petrochemical complexes, are sometimes sent via the fuel main to be burnt. The PSA process provides a low cost method of increasing the availability of high purity hydrogen and providing better utilisation of these “waste” streams.

Specialist design

Howe-Baker International Ltd is a specialist process design and management contractor operating in the oil production, refinery, power generation and petrochemical markets. For decades we have been supplying process plants to major worldwide refineries/operators and multinational engineering companies. Howe-Baker use their own proprietary technology and can also design, supply and erect plants for either hydrogen purification by PSA or hydrogen generation by steam reforming or methanol cracking.

Howe-Baker use 3-D Modelling to develop detailed designs for various process units. The modelling includes a full reality walk through facility allowing safety operations and maintenance operation aspects to be reviewed. Units are fully tested for rapid installation on the client’s prepared foundation.

Process

The PSA process involves the adsorption of impurities from a hydrogen rich feed gas onto a fixed bed of adsorbents at high pressure. The impurities are subsequently desorbed at low pressure into an offgas stream thereby producing an extremely pure hydrogen product. Product purities in excess of 99.999% can be achieved.

Various hydrogen rich feedstocks can be treated, including steam reformer syngas, methanol cracker syngas, refinery gases, ethylene cracker gas or coke oven gas. Applications that consume or generate hydrogen include propane dehydrogenation, linear alkyl benzene, gas to liquids (GTL). The PSA process is tailored to suit the feedgas composition and purity requirements by manipulating the cycle and adsorbents used.

1. Adsorption

Feed gas is passed co-currently through the clean adsorbent bed where impurities are selectively adsorbed. Pure hydrogen product at high pressure exits the bed.

4. Purge

At low pressure the bed is cleaned using a hydrogen rich stream obtained from another adsorber during co-current depressurization. Impurities are removed into the offgas stream.

2. Co-current depressurization

After adsorption the bed is saturated with impurities and requires regenerating.  To recover hydrogen trapped in the voice spaces, co-current depressurization passes hydrogen into repressurizing beds.

5. Counter-current repressurization

To prepare the bed for adsorption it is repressurized with hydrogen rich gas from a depressurizing adsorber and pure hydrogen product.

3. Counter-current depressurization

Final depressurization is counter-current and blows down impurities into the offgas stream.

The PSA process involves the adsorption of impurities from a hydrogen rich feed gas onto a fixed bed of adsorbents at high pressure. The impurities are subsequently desorbed at low pressure into an offgas stream, thereby producing an extremely pure hydrogen product. Product purities in excess of 99.999% can be achieved.

Various hydrogen rich feedstocks can be treated, including steam reformer syngas, methanol cracker syngas, refinery gases, ethylene cracker gas or coke oven gas. Applications that consume or generate hydrogen include propane dehydrogenation and linear alkyl benzene gas to liquids (GTL). The PSA process is tailored to suit the feedgas composition and purity requirements by manipulating the cycle and adsorbents used.

Operation

The PSA process is controlled by a PLC which manipulates the switching valves in a predetermined sequence. The plant is continually tuned to account for changes in feed flow and composition.

Through the use of monitoring and sophisticated plant diagnostics, the control system is able to identify any problems with the process, locate the source and alert the operator. If required, the plant can operate with a reduced number of adsorbers to allow online maintenance and increase plant availability.

Key benefits

Key reasons on why you should select Howe-Baker International Ltd for your next hydrogen PSA include:

  • Reliable, proven design
  • Fully guaranteed process
  • Cost effective solution
  • Modular construction
  • Comprehensive after sales service

Besides offering our standalone PSA units for purifications of hydrogen, we are in the enviable position of being able to offer fully integrated PSA and reformer technology, providing a single source design for the complete hydrogen plant.

Applications

  • Refinery
  • Petrochemicals
  • Vegetable oils
  • Paper & textiles
  • Steel industry
  • Fuel cells