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. The company have been supplying process plants to multinational engineering companies and major owner/operators worldwide for more than 20 years. 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.

Although the process is a batch operation, continuous product and offgas flows are achieved by using multiple adsorbers operated in a stepwise manner.  No matter how complex the PSA sequence it can always be broken down into the following 5 fundamental steps.

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.

2. Co-current depressurization

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

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.

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.

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.

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.