Core challenges and corresponding requirements

1. Start-up at low temperatures 

Main issues :

The ambient temperature is extremely low. On the one hand , the temperature of the exhaust gas will gradually decrease during the transmission process , and may even drop below 0°C. On the other hand, traditional catalysts have very low activity at low temperatures , and the preheating required to reach activation consumes a large amount of thermal energy .

Requirements for catalysts:

Catalyst systems with good low-temperature activity must be selected , such as noble metal catalysts (Pt, Pd) , whose preheating activation temperature can be as low as 150-200°C or even lower. Alternatively, high-performance transition metal oxides , such as certain specially designed manganese-based or composite oxides, can achieve the same effect and can be considered as an economical alternative .

2. Immense thermal stress and thermal shock

Main issues :

difference between starting exhaust gas emission operations at extremely low temperatures and rapidly heating the system to the reaction temperature can reach over 400°C, generating enormous thermal stress . Furthermore , when the system shuts down, the sudden drop from high to extremely low temperatures also generates significant thermal shock.

Requirements for catalysts:

The catalyst support (especially the honeycomb structure) needs to have extremely high thermal shock stability , requiring the use of materials with ultra-low coefficients of thermal expansion (such as high-quality cordierite). Furthermore, the bond between the active coating and the support must be extremely strong to prevent peeling and pulverization under severe thermal expansion and contraction. It is recommended to request a thermal shock test report from the supplier during procurement to demonstrate that the catalyst has undergone multiple runs without showing significant cracks under conditions ranging from high-temperature operating environments to extremely low room temperature after shutdown .

3. Icing, frosting, and physical blockage

Main issues :

Moisture generated after exhaust gas treatment can condense and freeze in pipes, valves, and catalyst beds, causing blockages in airflow channels . Additionally, the scrubbing fluid and lubricant in the exhaust gas pretreatment unit may freeze.

Requirements for the overall system:

On the one hand, the catalyst support (especially honeycomb ceramic) needs to be hydrophobically treated to reduce the risk of water adhesion and ice crystal growth in the pores.

On the other hand, the entire system needs to be designed to prevent freezing , and the heat tracing and insulation should be properly matched. The entire path from the exhaust gas inlet to the catalyst bed outlet (pipelines, valves, filters, reactor shell) must be equipped with full-process electric or steam heat tracing and wrapped with high-performance insulation materials to ensure that the gas temperature is always maintained above 10°C.

Finally, the entire reactor and piping system needs to be designed with a certain slope and equipped with steam traps or high-temperature drain valves to ensure that any possible condensate can be drained in a timely manner. In addition, the hydraulic oil used in the system and the washing liquid in the pretreatment unit must be low-temperature antifreeze type .

4. Energy supply fluctuations and safe start-up/shutdown

Main issues :

Extreme cold weather can affect the stability of power supply, leading to unplanned outages. If not handled properly, unreacted contaminants or condensate can remain inside the catalyst, causing corrosion or blockage.

Requirements for the overall system:

01 Equipped with UPS or backup power supply , critical control systems and heat tracing systems should be supported by uninterruptible power supply or backup generator.

02. An emergency shutdown procedure must be set up , and an emergency purging system driven by a backup power source must be provided. In the event of a power outage, the system should be automatically or manually activated to introduce hot nitrogen or hot air into the catalyst bed to purge residual contaminants and moisture until the temperature safely drops to ambient temperature.

03. The temperature rise and fall should be set slowly . The start-up preheating and shutdown cooling rates must be programmed and controlled to avoid excessively rapid temperature changes.

Design recommendations for catalytic reaction systems 

1. Enhance the preheating and heat recovery system

01 High-power preheater:

Configure a high-power electric heater or gas heater to heat the low-temperature exhaust gas to the temperature at which the catalyst operates normally in the shortest possible time .

02 High-efficiency heat exchanger:

A high-efficiency heat recovery heat exchanger is configured to preheat the intake air with the high-temperature gas after the catalytic reaction, thereby significantly reducing preheating energy consumption. In addition, the heat exchanger needs to be specially designed to prevent icing on the low-temperature side .

2. System equipment matching

01 Overall Configuration:

For all components that come into contact with gas (pipelines, flanges, valves, reactors , etc. ), it is recommended to choose low-temperature carbon steel or low-temperature resistant stainless steel with good low-temperature brittleness performance .

02 Instrument Configuration :

All monitoring and control instruments (temperature, pressure, flow , etc. ) must be compatible with an extremely wide operating temperature range (e.g., -50°C to +200°C). The overall control system must integrate anti-freeze logic, continuously monitor the temperature of critical points, and automatically increase the heating power or issue an alarm once the temperature approaches the freezing point.

3、Operations and maintenance training

System maintenance personnel need to receive specialized training , with particular emphasis on start-up and shutdown procedures in extremely cold weather , as well as emergency drills for sudden power outages and other emergencies .