Gas analyzers play crucial role in effective hydrogen production
Whether measuring, monitoring or controlling, steam methane reformers (SMRs) meet main gas analysis requirements
Demand for hydrogen is set to grow at a significant rate. According to Grand View Reasearch, the global hydrogen generation market size was valued at $120.77 billion in 2020 and is expected to expand at a compound annual growth rate (CAGR) of 5.7% from 2021 to 2028. An exponential increase in the demand for clean and green fuel due to rising pollution levels, coupled with growing government regulations to control and curb the sulphur content in fuels, is expected to drive this growth.
With this in mind, the oil and gas industry is constantly looking at ways to access a reliable and low-cost supply of high-purity hydrogen.
Popularity of SMR
Hydrogen can be produced through biological, electrolytic and thermochemical processes. The main method of producing hydrogen is through the thermochemical process, steam methane reforming (SMR), also known as methane/natural gas reforming. It is the most cost-effective method for hydrogen production, and consequently, much of the installed base of SMR plants is linked to refinery operations.
Steam reforming is endothermic — that is, heat must be supplied to the process for the reaction to proceed. This takes the form of high temperature steam, which is used to produce hydrogen from a methane source, typically natural gas. The methane reacts with the steam under a pressure of between three to 25 bar in the presence of a catalyst.
The products of this reaction are hydrogen and carbon monoxide (CO) with a small amount of carbon dioxide (CO2). In a further stage, known as the water-gas shift reaction, the carbon monoxide and steam are reacted to produce carbon dioxide and more hydrogen. The carbon dioxide and other impurities are then removed to leave mostly pure hydrogen.
And while this is a relatively mature technology, it is expected to grow further in the short term. According to 360 Research Reports, the global SMR market is valued at $676.5 million in 2020 is expected to reach $1014.9 million by the end of 2026, growing at a CAGR of 5.9% during 2021-2026.
The key role of gas analyzers
Gas analyzers are viewed by many as key in helping the SMR process to maximize hydrogen production while minimizing the consumption of feedstocks and hydrocarbon. This efficiency improvement, driven through the use of instrumentation to measure temperature and pressure and analyze gas compositions, also helps the SMR process to produce fewer emissions of gases such as CO2, nitrogen oxide (NOx,) sulphur oxide (SOx) and particulate matter.
Some of the most fundamental gas analysis requirements on an SMR process are:
- Calculation of the calorific British Thermal Unit (BTU) value of the incoming feedstock
- Monitoring methane slip through the SMR
- Controlling the steam-to-carbon ratio in the SMR
- Measurement of the final hydrogen product purity
- Measurement of the reformer burner flue gas oxygen concentration.
Meeting these requirements demands a wide range of gas analyzers based on different technologies and having varied features and levels of precision to suit the application.
The first task is to decide what the most essential functionality is for each measurement stage in the process. For example, this could be continuous and instantaneous measurement of a specific type of molecule. Alternatively, a range of gases may need measuring, but for which an instantaneous reading is not required.
This can be illustrated with the requirements for the calculation of BTU for the feedstock. This is best achieved with a rapid response process gas chromatograph for SMR feed gas analysis. The instrument needs the ability to analyze the mixed composition of the natural gas stream. This can contain a variety of light hydrocarbons, including ethane and propane as well as methane. In some cases, the SMR can be fed with refinery gas, which can contain a highly diverse mix of fuel gases.
Fitted with a thermal conductivity detector (TCD), such an instrument would be ideal for determining the BTU value of natural gas or naphtha feed to SMRs. A good instrument should be able to analyze and characterize a gas mixture sample every two minutes. Analysis of the gas composition then allows the BTU to be calculated.
Direct read analyzers
Unlike the intermittent analysis that is adequate for calculating BTU value, direct reading instruments are electronic devices that provide a rapid or continuous detection or measurement of the concentration of the compound in question.
They provide continuous information allowing every change in the process to be observed. This enables the control system to react within seconds to ensure that the process can be continuously optimized.
One of the major uses for a direct read instrument in an SMR process is to detect methane slip. Methane should be reacted to CO2, CO and hydrogen in the SMR. If excessive amounts of methane slip through the process, this can be a clear sign that something is wrong.
Since methane is infrared active, absorbing infrared light, it can be detected using a non-dispersive infra-red (NDIR) analyzer. These instruments are flexible enough to be used across a range of gases including CO, CO2, methane and other light hydrocarbons. If the analyzer detects excessive amounts of methane slipping through the process, this could indicate that the catalyst needs replacement. An alternative cause is low temperatures in the SMR. This can be solved by increasing the amount of fuel gas supplied to the burners.
Although some of these factors, such as the performance of the catalyst, are longer term, others such as temperature changes can occur rapidly. A direct read instrument will help to fix the issue with minimal delay.
The steam-to-carbon ratio is one of the most important measurement areas in the SMR process. Controlling this ratio correctly gives significant increases in the unit’s efficiency. Typically, the ratio must be above 3:1 to prevent carbon deposition on the catalyst.
One of the recognized ways of controlling this ratio is using a gas chromatograph analyzer and orifice plate. Alternative methods include using an NDIR analyzer.
NDIR analyzers are also ideal for measurement of the final hydrogen purity, even though hydrogen is not IR active and is not detectable on an NDIR. Although most of the gas coming off the SMR will be hydrogen, the most significant factor is the absence of CO and CO2, which are detectable by NDIR instruments. These two gases are poisonous to the hydro-treating catalysts in the subsequent processes where the hydrogen is used in the refinery.
The final hydrogen product specification should ideally have a maximum total combined CO and CO2 content of 10 parts-per-million by volume (VPM).
The measurement of flue gas oxygen is usually based on a zirconium oxide cell. One instrument mounts this at the tip of the probe that is inserted into the flue duct. This gives a direct, in situ measurement, providing an accurate and rapid oxygen reading to help optimize combustion control.
A measured future
The digitalization of gas analyzers is a game changer in helping to offer facilities such as remote operations, self-diagnosis and automatic calibration. This, coupled with the use of condition monitoring services, have the potential to support oil and gas companies as they work towards meeting the future demand of hydrogen through efficient SMR.