Plate catalyst

Plate catalyst is an SCR catalyst geometry built from parallel catalyst-coated plates rather than extruded ceramic honeycomb cells. The plates are assembled into modules with open channels that let flue gas, ammonia, NOx, and dust pass through the reactor while the catalytic surface drives the reduction reaction.

Plate catalyst is common in high-dust coal, biomass, waste, and heavy industrial service. The wider passages tolerate larger ash particles and irregular deposits better than tight honeycomb cells. The tradeoff is lower geometric surface area per unit volume, so reactor depth, catalyst volume, and pressure drop must be designed accordingly.

Operating role

In a selective catalytic reduction reactor, ammonia or urea-derived ammonia is mixed into the flue gas upstream of the catalyst. On the catalyst surface, NOx reacts to form nitrogen and water. The plate geometry must provide enough residence time and active surface while keeping velocity, pressure drop, ammonia distribution, and ash deposition within limits.

High-dust SCR units usually sit upstream of the air heater and particulate collector. That position gives good temperature for the catalyst but exposes it to fly ash, large-particle ash, popcorn ash, unburned carbon, and alkali salts. Poor flow distribution or ammonia mixing can cause local overloading, masking, erosion, or ammonium bisulphate formation.

Failure modes

Plate catalyst can plug, blind, erode, poison, or deactivate. Pluggage occurs when ash bridges channel openings. Masking covers the active surface with a dust or salt film. Erosion cuts coating from leading edges. Chemical poisoning can come from arsenic, alkali metals, phosphorus, or other trace species depending on the fuel. Thermal excursions can also reduce catalyst life.

Operators track reactor pressure drop, NOx reduction, ammonia slip, catalyst sample activity, ash loading, and temperature profile. A pressure-drop rise with stable inlet dust often points to deposition or poor cleaning. Rising ammonia slip at the same NOx set point can indicate loss of activity or maldistribution.

Acoustic cleaning context

Sonic horns are widely considered for plate catalyst because the open channels can transmit acoustic energy and release dry dust before it consolidates. They are normally arranged to sweep the catalyst face or module rows without creating direct erosion. Acoustic cleaning is most effective as frequent preventive cleaning; it is less effective after deposits have sintered, become sticky, or chemically bonded to the catalyst.

Design and maintenance context

Plate catalyst modules are specified around gas velocity, pitch, active material loading, pressure drop, ammonia distribution, expected ash burden, and the temperature window required for the reaction. Wider passages tolerate more ash and are easier to keep open, while tighter passages may give more active area in the same reactor volume. The choice is therefore tied to sootblowing, acoustic cleaning, upstream ash carryover, and the economic cost of pressure drop.

Inspection programmes look for leading-edge erosion, fly ash masking, ammonium-salt fouling, cracked plates, seal bypass, frame distortion, and uneven colour or texture that suggests maldistribution. Operators compare NOx reduction, ammonia slip, reactor pressure drop, catalyst samples, and temperature profiles to decide whether lost performance is caused by poisoning, plugging, ageing, or poor reagent mixing. Cleaning systems are most useful when the problem is loose particulate on the catalyst face. If alkali, arsenic, sulphur compounds, or thermal sintering have damaged the active surface, the remedy is regeneration or replacement rather than stronger cleaning.

Cleaning acceptance

For plate catalyst, cleaning success should be judged by face condition, layer pressure drop, NOx reduction, and ammonia slip together. A clean-looking face is not enough if reagent distribution remains poor or if active sites have been poisoned. Sampling and laboratory activity tests may be needed when visual inspection and performance trend disagree.

Acoustic cleaners are most useful when they prevent loose ash from settling at the leading edge and between plates. They should be commissioned with hopper checks because ash that leaves the catalyst face still has to leave the reactor. If hopper discharge is unreliable, cleaning can simply move the plugging problem downward.

Related terms

• Selective Catalytic Reduction
• Honeycomb catalyst
• Corrugated catalyst
• Catalyst pluggage