Improving the NOx reduction performance of an Euro VI d SCR System in real-world condition via nonlinear model predictive control

This paper deals with the possibility of improving the urea dosage control for the Selective Catalytic Reduction Systems (SCR) of an Euro VI d diesel light commercial vehicle in order to increase [Formula: see text] after-treatment reduction performance. To this aim, first, we assess the effective emissions abatement performance for the appraised diesel vehicle via real-world experimental campaign, carried out according to the Real Driving Emissions (RDE) tests on urban, extra-urban and motorway road sections in Naples, Italy. Based on these real-world data, we derive a parameterized control-oriented model for the SCR system which is, then, exploited for the designing of an alternative urea injection logic which could be able to maximize the [Formula: see text] reduction efficiency while minimizing tailpipe ammonia slip. Specifically, the optimal AdBlue injection rate is designed according to a Nonlinear Model Predictive Control Approach which allows obtaining a proper trade-off between the [Formula: see text] abatement and the urea overdosing problem. The effectiveness of the proposed controller is evaluated by comparing the performance assessed for the appraised SCR system during the experimental tests with the ones achievable if the Euro VI diesel would be equipped with the proposed control strategy. Numerical simulation discloses the effectiveness of the NMPC controller in ensuring improved [Formula: see text] reduction with performance complying with the emissions norms, main in avoiding excessive ammonia slip and in guaranteeing a reduced feed ratio w.r.t. to the standard industrial SCR controller mounted on the vehicle.

Combined NOx and NH3 Slip Reduction in a Stoker Boiler Equipped with the Hybrid SNCR + SCR System FJBS+

The application of secondary NOx control methods in medium to low-capacity furnaces is a relatively new topic on the energy market and thus requires further research. In this paper, the results of full-scale research of SNCR and hybrid SNCR + SCR methods applied into a 29 MWth solid fuel fired stoker boiler is presented. The tests were performed for a full range of boiler loads, from 33% (12 MWth) to 103% (30 MWth) of nominal load. A novel SNCR + SCR hybrid process was demonstrated based on an enhanced in-furnace SNCR installation coupled with TiO2-WO3-V2O5 catalyst, which provides extra NOx reduction and works as an excess NH3 “catcher” as well. The performance of a brand-new catalyst was evaluated in comparison to a recovered one. The emission of NOx was reduced below 180 mg NOx/Nm3 at 6% O2, with ammonia slip in flue gas below 10 mg/Nm3. Special attention was paid to the analysis of ammonia slip in combustion products: flue gas and fly ash. An innovative and cost-effective method of ammonia removal from fly ash was presented and tested. The main idea of this method is fly ash recirculation onto the grate. As a result, ammonia content in fly ash was reduced to a level below 6.1 mg/kg.

Ammonia Slip Estimation Based on ASC Control-Oriented Modelling And OBD NOx Sensor Cross-Sensitivity Analysis

The incoming emission regulations for internal combustion engines are gradually introducing new pollutant species, which requires greater complexity of the exhaust gas aftertreatment systems concerning layout, control and diagnostics. This is the case of ammonia, which is already regulated in heavy-duty vehicles and to be included in the emissions standards applied to passenger cars. The ammonia is injected into the exhaust gas through urea injections for NOx abatement in selective catalytic reduction (SCR) systems and can be also generated in other aftertreatment systems as three-way catalysts. However, ammonia slip may require removal on a dedicated catalyst called ammonia slip catalyst (ASC). The set consisting of the urea injection system, SCR and ASC requires control and on-board diagnostic tools to ensure high NOx conversion efficiency and minimization of the ammonia slip under real driving conditions. These tasks are based on the use of NOx sensors ZrO2 pumping cell-based, which present as a drawback high cross-sensitivity to ammonia. Consequently, the presence of this species can affect the measurement of NOx and compromise SCR-ASC control strategies. In the present work, a methodology to predict ammonia and NOx tailpipe emissions is proposed. For this purpose, a control-oriented ASC model was developed to use its ammonia slip prediction to determine the cross-sensitivity correction of the NOx sensor placed downstream of the ASC. The model is based on a simplified solution of the transport equations of the species involved in the main ASC reactions. The ammonia slip model was calibrated using steady- and quasi-steady-state tests performed in a Euro 6c diesel engine. Finally, the performance of the proposed methodology to predict NOx and ammonia emissions was evaluated against experimental data corresponding to Worldwide harmonized Light vehicles Test Cycles (WLTC) applying different urea dosing strategies.

Deactivation of V2O5−WO3/TiO2 DeNOx Catalyst under Commercial Conditions in Power Production Plant

Nitrogen dioxide is one of the most dangerous air pollutants, because its high concentration in air can be directly harmful to human health. It is also responsible for photochemical smog and acid rains. One of the most commonly used techniques to tackle this problem in large combustion plants is selective catalytic reduction (SCR). Commercial SCR installations are often equipped with a V2O5−WO3/TiO2 catalyst. In power plants which utilize a solid fuel boiler, catalysts are exposed to unfavorable conditions. In the paper, factors responsible for deactivation of such a catalyst are comprehensively reviewed where different types of deactivation mechanism, like mechanical, chemical or thermal mechanisms, are separately described. The paper presents the impact of sulfur trioxide and ammonia slip on the catalyst deactivation as well as the problem of ammonium bisulfate formation. The latter is one of the crucial factors influencing the loss of catalytic activity. The majority of issues with fast catalyst deactivation occur when the catalyst work in off-design conditions, in particular in too high or too low temperatures.

Study on Formation, Deposition and Fouling Prediction of Ammonium Bisulfate (ABS) at Air Preheater in Utility Boiler

The ammonium bisulfate (ABS) widely exists at air preheater. The ABS may deposit and foul at the heating elements of air preheater because of the chemical reaction between SO3 at flue gas side and ammonia slip from SCR excess injection. The heat transfer equation between flue gas side and air side is constructed and simplified using physical and mathematical models accordingly. The finite difference method is applied to solve numerically by means of iterative computation. Based on the NH3 and SO3 concentration data from the real time data in the actual operation and the discrete calculation of the temperature field, the Radian number (Ra) is used to evaluate the possibility of ABS fouling and the developing trend of heating elements at the air preheater. A 1000MW ultra supercritical boiler is selected as example. The ABS deposit area is simulated under different working conditions 100%BMCR, 75% BMCR and 50% BMCR. The possible ABS deposition and fouling is analyzed for operators to evaluate the risk of cold-end and hot-end heating elements plate at air preheater. As the working load decreases lower than 50%BMCR, the deposition and fouling position could extend to the hot-end area of heating elements at air preheater.