What is an SCR unit and how does a diesel SCR system work?
An SCR unit (Selective Catalytic Reduction system) reduces NOx in diesel exhaust by dosing DEF/AdBlue upstream of an SCR catalyst. Correct sizing, temperature and control are essential.
How an SCR system works
The dosing module injects a calibrated amount of DEF into the exhaust. Under suitable thermal conditions, ammonia is formed and reacts with NOx across the SCR catalyst, producing mainly nitrogen and water.
Main components
- SCR catalyst.
- DEF/AdBlue tank and supply circuit.
- Dosing module and injector.
- Temperature and, where required, NOx sensors.
- Electronic control and diagnostics.
SCR, DPF and DOC are not interchangeable
SCR targets NOx. A DPF captures particulate matter, while a DOC primarily oxidises CO and hydrocarbons. Demanding applications may require a combined architecture.
Industrial and mining applications
Underground mining equipment, tunnel machinery, rail maintenance vehicles and heavy off-road machines require application-specific thermal and mechanical engineering. NOxBUSTER® combines DPF and SCR for simultaneous NOx and particulate control.
SCR unit components
- SCR catalyst
- DEF/AdBlue tank, pump and dosing injector
- Temperature and NOx sensors where required
- Electronic control and diagnostics
SCR units for mining, heavy equipment and rail
SCR retrofit is used where NOx reduction is required on existing diesel assets. Typical applications include mining equipment and heavy equipment.
SCR + DPF
When NOx and particulate matter must both be reduced, SCR is combined with a DPF. See NOxBUSTER®.
Frequently asked questions
Does SCR remove particulate matter?
Not as its primary function. A diesel particulate filter is normally required when particulate control is also needed.
Can SCR be retrofitted to older machinery?
It may be feasible after assessing exhaust temperature, duty cycle, packaging, control and maintenance requirements.