Technical glossary: high-temperature filtration and diesel emissions
Concise definitions of the terms used in high-temperature flue gas filtration, diesel exhaust aftertreatment and emission rules.
High-temperature flue gas filtration
High-temperature flue gas
Dust-laden gas from industrial kilns, boilers, smelters and incinerators, typically above 200 C. The upper temperature limit dictates the filter media and cleaning method, and is the first constraint in system design.
Metal filter bag
A flexible filter bag made from sintered metal fibre felt, serviceable above 500 C and fully recyclable. Under high-temperature, corrosive duty it can hold emissions stably below 5 mg/Nm3.
Ceramic fiber filter tube
A rigid filter element made of ceramic fibre, resistant to high temperature and acid attack. It is widely used for flue gas from waste incineration, glass and metallurgical furnaces.
Membrane filter media
Filter media with a microporous membrane, usually PTFE, laminated to the surface. Filtration takes place at the surface, so dust does not penetrate the substrate, giving higher capture efficiency and cleaner cleaning.
Air-to-cloth ratio
The volume of gas passing through unit filter area per unit time, also called filtration velocity. A higher value shrinks the equipment but raises pressure drop, abrasion and emission risk.
Pressure drop
The differential pressure across the filter media, which drives fan power consumption. Holding it within a stable band through proper cleaning is the key to economical baghouse operation.
Pulse-jet cleaning
Cleaning by a short compressed-air pulse that dislodges the dust cake from the bag. It is the mainstream method for baghouses, and intensity depends on pulse pressure and duration.
Bag blinding
Irreversible loss of permeability when dust embeds in the media or condensate glues it shut, so cleaning no longer works. Typical causes are dew-point operation, oil mist and overheating.
Diesel exhaust aftertreatment
Diesel particulate filter (DPF)
A filter in the diesel exhaust system that traps soot and the soluble organic fraction. Trapped particles must be oxidised through regeneration, otherwise back pressure keeps rising.
Diesel oxidation catalyst (DOC)
A precious-metal coated catalyst that oxidises CO, HC and part of the NO in the exhaust, converting NO to NO2 and thereby enabling passive regeneration of the downstream DPF.
Selective catalytic reduction (SCR)
Urea solution is injected into the exhaust and, over a catalyst, reduces NOx to nitrogen and water. It is the mainstream route for heavy-duty engines to meet China VI and Euro 7 NOx limits.
Ammonia slip catalyst (ASC)
An oxidation catalyst downstream of the SCR that removes unreacted ammonia slip, preventing secondary ammonia emissions.
Passive regeneration
Continuous oxidation of soot in the DPF using exhaust heat and the oxidising power of NO2 during normal operation, with no external energy input.
Active regeneration
Forced soot burn-off achieved by raising exhaust temperature above the soot ignition point, using post-injection, electrical heating or a burner.
Back pressure
The resistance the aftertreatment system imposes on exhaust flow. Excessive back pressure cuts power and raises fuel consumption and temperature, and is the key constraint in DPF matching.
Ash accumulation
Non-combustible ash from burnt lubricant additives collects in the DPF channels. Regeneration cannot remove it, so periodic cleaning sets the real service life of the filter.
Emission rules and standards
China IV and China VI
Chinese emission stages for heavy-duty vehicles and non-road machinery, tightening NOx and particulate limits step by step. China VI adds on-board diagnosis and remote monitoring.
Non-road mobile machinery
Diesel equipment that does not travel on public roads, such as construction, port and mining machinery and generator sets, regulated under separate emission rules.
Euro 7
The new EU emission regulation, phased in from 2026. Beyond tailpipe limits, it regulates brake and tyre wear particles for the first time.
Stationary source emissions
Emissions from fixed installations such as power plants, kilns and incinerators, governed by industry-specific limits and test methods, separate from mobile-source rules.
Emission concentration
Pollutant mass per unit volume of dry flue gas, expressed in mg/Nm3. Values are comparable only when the reference oxygen content and correction basis are stated.
Conversion efficiency
The share of inlet pollutant removed across a device, the core metric for judging DPF, DOC and SCR performance.
Secondary pollution
Pollution generated by the treatment process itself, such as spent bags, spent catalyst, ammonia slip and washing wastewater, which must be addressed in the same plan.
Flue gas conditioning
Pre-treatment that adjusts gas temperature, moisture and acid dew point by water or alkaline injection or sorbent dosing, keeping media and equipment within safe operating limits.