|Abstract Title:||SNCR and NH3 measurements in the cement industry|
|Session Choice:||Continuous Emission Monitoring|
|Presenter Name:||Mr Abhijit Chatterjee|
|Co-authors:||Mr Angshuman Paul|
|Company/Organisation:||Adage Automation Private Limited|
Abstract Information :
Adage Automation is one of the leaders in the Gas Analytics for Cement Process and is amongst the few manufacturers of kiln inlet systems in the world. ABHIJIT CHATTERJEE speaks about some of these analysers.
Indian cement plants have undergone major changes in the recent past primarily for process improvement and reduction in the emissions. Growth of any nation depends on the success story of certain key industry sectors and cement is one of them.
With installations of gas analyser systems in the cement Industry domain across 40 countries around the world, Adage enjoys a leadership position in the Indian cement Industry in terms of market share and innovation.
Today, there are two major types of DeNOx processes known in industry: the Selective Catalytic Reduction (SCR) and the Selective Non-Catalytic Reduction (SNCR). SCR DeNOx installations are common for large scale combustion plants like coal fired power utilities, whereas SNCR technology can often be found in large to mid-size cement plants and incineration plants. LDS 6 insitu Laser Gas analyzers can be used for optimisation of either technology.
The SNCR process
In the SNCR process, usually ammonia (NH3) or urea (CO(NH2)2) is introduced to the flue gases in the hot combustion zone where the reduction of NOx takes place spontaneously. Depending on the type of the reducing agent used, the SNCR process is usually operated in the temperature range of 800 to 950°C. At temperatures below the optimum temperature, the reaction rate is too slow, resulting in an inefficient NOx reduction and high ammonia slip. Above the optimum temperature, the oxidation of ammonia to NOx is getting significantly high and the process tends to produce NOx instead of decreasing it.
As combustion processes normally show fast and considerable changes in the temperature distribution and the composition of the flues gas, the efficiency of the SNCR- DeNOx process is strongly dependent on the temperature and NOx distribution in the reaction zone.
At constant NOx level behind the reaction zone, the NH3 slip is a strong indicator of the current reaction conditions.
Ammonium isulphate formation
Together with acidic flue gas components, the NH3 injected to the flue gas (or formed from an injected ammonia derivative like urea) can lead to salt formation. Mainly ammonium bi-sulphate (ABS) causes difficulties in the process:
- ABS has a melting point of 147°C and will consequently be present as a liquid or solid accumulated on surfaces.
- It might plug parts of the catalyst, increasing the pressure drop and causing catalyst deactivation. It might also plug the air pleater (AP), decreasing its efficiency.
- ABS is hygroscopic at lower temperatures and will cause corrosion when absorbing moisture from the gas.
- ABS formed on ash particles can cause sticky ash on the electrostatic precipitator's (ESP) hoppers which are problematic to handle.
A single LDS 6 analyser is able to monitor the NH3 slip in up to three measurement points simultaneously.
One sensor pair is used to control the ammonia concentration in situ directly after the catalyst or the high temperature reaction zone.
Since LDS 6 delivers NH3 concentration data in real-time, very fast control of the NH3 slip is achieved - runtimes with excess dosage are completely avoided.
Another important measuring point is the emission monitoring directly in the stack. Here, the final emission of NH3 and therefore the total nitrous emission is observed. Siemens LDS 6 advantage for DeNOx control :
Faster regulation than with other available technologies (e.g., FTIR) and therefore most efficient optimisation. The in situ approach allows representative NH3 measurements without side effects or cross interference. The patented inbuilt calibration cell allows ease of maintenance.
Optimising an SNCR process by controlling the NH3 slip means:
- To reduce the consumption of ammonia or urea while keeping the legislative threshold values for NOx (and NH3 if required);
- To stabilise the process and avoid peak emissions
- To minimise technological drawbacks, increasing DeNOx ef?ciency at reasonable level of NH3 slip
- To reduce the total nitrogen - NH3 and NOx - emission.
- In-situ technology with fast response time
- No sampling system
- Separation of analyser and process environment
- High resistance to corrosion & measurements are feasible in high dust loads and complex gas mixtures
- Built-in calibration cell
- Lifelong calibrated analyzer & zero and span checked 24 timess
- Multi -points: Up to three measurement locations can be monitored in the same time
- Laser technology
- No cross interference