on-site steam Reforming

The Steam Reformer Process

The process is divided into the generation of a hydrogen rich reformate stream by means of steam-methanereforming (SMR) and the following hydrogen purification by means of pressure swing adsorption (PSA).
The process route consists mainly of

• Pre-Treatment of the Feed
  The hydrocarbon feedstock is desulphurised using e.g. activated carbon filters, pressurised and, depending on the reformer design, either preheated and mixed with process steam or directly injected with the water into the reformer without the need of an external heat exchanger. The fresh water is first softened and demineralised by an ion-exchange water conditioning system. One option is high pressure reforming with integrated heat exchangers and a working pressure of up to 16 bar which reduces the geometric volume of the reformer vessels and is ideal for a downstream treatment by means of PSA or compression. The other option is to operate the reformer at low pressures (1.5 bar) with an increased conversion ratio and compress the reformate prior to purification.
• Steam Reforming and CO-Shift Conversion
  Methane and steam are converted within the compact reformer furnace at approx. 900 °C in the presence of a nickel catalyst to a hydrogen rich reformate stream according to the following reactions: (1) CH4 + H2O CO + 3 H2 (2) CO + H2O CO2 + H2 • The heat required for reaction (1) is obtained by the combustion of fuel gas and purge/tail gas from the PSA system. • Following the reforming step the synthesis gas is fed into the COconversion reactor to produce additional hydrogen. Heat recovery • for steam or feedstock preheating takes place at different points within the process chain to optimise the energy efficiency of the reformer system (depending on the reformer design).
• Gas Purification – PSA-System
  Hydrogen purification is achieved by means of pressure swing adsorption (PSA). The PSA unit consists of four vessels filled with selected adsorbents. The PSA reaches hydrogen purities higher than 99.999 % by volume and CO impurities of less than 1 vppm (volumetric part per million) fulfilling the specifications set by the fuel cell bus supplier. Pure hydrogen from the PSA unit is sent to the hydrogen compressor, while the PSA off-gas from recovering the adsorbents, called tailgas, is fed to the reformer burner. Depending on the reformer design, a recuperative burner is used featuring high efficiency and low nitrogen oxide (NOx) emissions. During normal operation, the burner can be operated solely on the tailgas stream.

Steam Reformer Units in the HyFLEET:CUTE Project

Two cities, Madrid and Stuttgart, have installed small scale steam reforming plants onsite. These units were delivered by Carbotech GmbH for Madrid and Mahler IGS for Stuttgart. The reformers have a projected thermal efficiency of near to 65 % based on the lower heating values of natural gas and hydrogen. In Madrid, road supply of hydrogen and on-site production run in parallel. Because of the supplementary external hydrogen source, the reformer design capacity (50 Nm3/h) could be determined below the rated demand of all fuel cell buses (75 Nm3/h, HuFLEET:CUTE project and one additional vehicle). This allows longer periods of reformer operation at full load and reduces the number of start-stop cycles when not all buses are in service.

Key Characteristics of the Installed Steam Reformer Technology

• The steam reforming plants are designed as turn-key solutions. They can either be built on skids or in one container, thus reducing the space requirement (a net area equivalent to max. two 20-foot containers including the PSA unit is needed) and the commissioning time. The only interfaces needed are natural gas, water and electricity supply.
• The modular construction allows a capacity extension of the plant whenever it may be required. This could be either realised by adding complete containerised reformer modules or by adding reformer tubes to the existing ones (no new reformer module necessary). • The plants are designed for automatic and unattended operation. This includes automatic start-up and shut-down and automatic load adjustment using a remote control system (e.g. via internet).
• Hydrogen quality is constantly monitored and guaranteed by the reformer suppliers. Safety-Related Key Characteristics
• The reformer plants are designed to meet the highest safety standards (EN regulations, CE labelling and EC directives). Should any safety related problem occur the systems will automatically switch into safe state.