The Linde Isothermal Reactor is a fixed bed reactor with indirect heat exchange suitable for endothermic and exothermic catalytic reactions. It represents one of the most effective and successful developments of the recent past. Due to the special design gas/gas, gas/liquid and liquid/liquid reactions can be carried out. For every process a special catalyst is used in a fixed bed reactor to get maximum yield of hydrogen product.
At the outlet of steam reformers, partial oxidation reactors or coke oven gas units, the syngas contains H2, CO, CO2, CH4 and water in chemical equilibrium at high temperatures in the range of 700 to 1400°C depending on the process pressure and the mixture of feedstock and process steam or water.
There are three different versions of CO shift conversion:
high temperature (HT) CO shift conversion at about 300 to 450 °C down to approx. 2.5 % CO on dry basis at the reactor outlet,
medium temperature (MT) CO shift conversion or so-called isothermal shift conversion at about 220 to 270 °C down to approx. 0.5 % CO on dry basis at the reactor outlet, and
low temperature (LT) CO shift conversion at about 180 to 250 °C down to approx. 0.2 % CO on dry basis at the reactor outlet.
The use of HT CO shift conversion is state of art in almost every hydrogen plant. The application of the low temperature CO shift conversion is normally installed downstream of the HT shift at already reduced CO content in the feed gas.
This additional investment is considered for plants witha capacity above approx. 40,000 Nm³/h H2 product. The catalyst of the LT shift is very sensitive against sulphur, chlorine and liquid water and special attention is required during start up and plant upset conditions.
In former concepts the LT shift was important because of the downstream methanisation of CO following the CO2 removal unit, to meet the product purity at minimum H2 losses. After the implementation of the Pressure Swing Adsorption (PSA unit) for H2 purification these process steps have become obsolete.
The MT CO shift conversion as isothermal reaction can be approximated in several adiabatic reactors with intercoolers or better in an isothermal reactor with integrated steam generation for cooling of the process gas. The temperature of the shift reaction is controlled easily by setting the pressure of the generated steam.