Techno-Economic Evaluation of Co-Removal of NOx and SOx Species from Flue Gases via Enhanced Oxidation of NO by ClO2—Case Studies of Implementation at a Pulp and Paper Mill, Waste-to-Heat Plant and a Cruise Ship

Co-absorption of NO2 and SO2 from flue gases, in combination with the enhanced oxidation of NO by ClO2(g), is studied for three different flue gas sources: a medium sized waste-to-heat plant; the kraft recovery boiler of a pulp and paper mill; and a cruise ship. Process modeling results are used to present the technical potential for each site together with cost estimation and optimization using a bottom-up approach. A process set-up is proposed for each site together with equipment sizing and resulting flows of process fluids. The simulation results, supported by experimental results, show that removal rates equal to or greater than current best available technologies are achievable with more than 90% of NOx and 99% of SO2 removed from the flue gas. The resulting cost of removing both NOx and SO2 from the flue gases is 2100 €/ton for the waste-to-heat plant, 800 €/ton for the cruise ship and 3900 €/ton for the recovery boiler. The cost estimation show that the consumption and cost of chemical additives will play a decisive role in the economic feasibility of the investigated concept, between 50% and 90% of the total cost per ton acid gas removed.

New learnings and strategies for meeting future recovery boiler particulate emission limits with existing electrostatic precipitators

It is foreseeable that recovery boiler particulate emission limits in the United States and Canada will continue to get more stringent with time. Because of this, continued improvement of emission control equipment, as well as a better understanding of how operating parameters affect performance, are necessary. Although electrostatic precipitators (ESPs) are often viewed as a mature technology, many improvements in ESP technology continue to be developed. In recent years, academic efforts have improved the understanding of recovery boiler operating conditions on ESP performance. Additionally, advancements in materials, power supplies, and design continue to improve the efficiency and reliability of ESPs. This paper discusses how recovery boiler and electrostatic precipitator (ESP) operating factors affect ESP performance based on process simulations and practical experience, and how these learnings can be implemented to improve future operation of existing ESPs.

Evaluation of the Energy Efficiency Improvement Potential through Back-End Heat Recovery in the Kraft Recovery Boiler

Sustainability and energy efficiency have become important factors for many industrial processes, including chemical pulping. Recently complex back-end heat recovery solutions have been applied to biomass-fired boilers, lowering stack temperatures and recovering some of the latent heat of the moisture by condensation. Modern kraft recovery boiler flue gas offers still unutilized heat recovery possibilities. Scrubbers have been used, but the focus has been on gas cleaning; heat recovery implementations remain simple. The goal of this study is to evaluate the potential to increase the power generation and efficiency of chemical pulping by improved back-end heat recovery from the recovery boiler. Different configurations of heat recovery schemes and different heat sink options are considered, including heat pumps. IPSEpro simulation software is used to model the boiler and steam cycle of a modern Nordic pulp mill. When heat pumps are used to upgrade some of the recovered low-grade heat, up to +23 MW gross and +16.7 MW net power generation increase was observed when the whole pulp mill in addition to the boiler and steam cycle is considered as heat consumer. Combustion air humidification proved to yield a benefit only when assuming the largest heat sink scenario for the pulp mill.

Development of simplified mathematical model of P-88 recovery boiler for operating modes at loads near the nominal

To improve the design of the elements of combined-cycle plants, and their structural and mode optimization, mathematical models are required. These models show energy efficiency indicators of the equipment under changing operating conditions. Modeling of recovery boilers is traditionally carried out with the application of specialized software systems that implement submodels of thermal-hydraulic calculations of the elements of the boiler water-steam and gas paths. This approach makes it difficult to solve practical tasks, since it requires licensed software and appropriate qualifications of an engineer. The current direction of solving this problem is statistical processing of the results of calculation data obtained with the application of specialized software systems, and development of a simplified mathematical model in the form of regression dependencies of boiler performance on variable parameters. In this study, the problem is solved in relation to the P-88 boiler of the combined-cycle plant-325 power unit in the load range near the nominal one. The initial mathematical model is developed with the application of the software package “TRAKT” designed for verification and engineering design of boilers. The simplified mathematical model is based on the methods of regression analysis of statistical data. The accuracy of the model is estimated based on the operational data of the combined-cycle plant -325 power unit. The authors have developed the mathematical model of the P-88 recovery boiler, which allows to determine the main performance indicators of the boiler when the electric power of the gas turbine and the outdoor air temperature are changing at the loads near the nominal value. The performance indicators are determined without application of specialized software for design calculation of the boiler. The accuracy of the initial mathematical model implemented in the software package “TRACT” is characterized by deviation of the calculation results data from the operational data in the corresponding modes of no more than 2 %. The additional uncertainty value introduced into the calculation results data does not exceed 1,5 % when we transfer from the initial mathematical model to the simplified one. The resulting mathematical description will allow solving the problems of mode optimization and evaluating the efficiency of the recovery boiler and the power unit under changing operating conditions.

Evaluation and analysis of exergoeconomic performance for the calcination process of green petroleum coke in vertical shaft kiln

The main objective of this paper is to establish a mathematical framework to analyze the complex thermal economic performance of the calcination process. To find the factors affecting exergy efficiency loss, different exergy destruction is investigated in detail. Furthermore, the exergy flow cost model for exergy cost saving has also been developed. The results show that the vertical shaft furnace is a self-sufficiency equipment without additional fuel required, but the overall exergy destruction accounts for 54.11% of the total exergy input. In addition, the energy efficiency of the waste heat recovery boiler and thermal deaerator are 83.52% and 96.40%, whereas the exergy efficiency of the two equipment are 65.98% and 94.27%. Furthermore, the import exergy flow cost of vertical shaft furnace, waste heat recovery boiler and thermal deaerator are 366.5197 RMB/MJ, 0.1426 RMB/MJ and 0.0020RMB/MJ, respectively. Based on the result, several suggestions were proposed to improve the exergoeconomic performance. Assessing the performance of suggested improvements, the total exergy destruction of vertical shaft furnace is reduced to 134.34 GJ/h and the exergy efficiency of waste heat recovery boiler is raised up to 66.02%. Moreover, the import exergy flow cost of the three different equipment is reduced to 0.0329 RMB/MJ, 0.1304 RMB/MJ and 0.0002 RMB/MJ, respectively.

THE ANALYSIS OF POSSIBLE FAULTS OF TECHNOLOGICAL PROCESSES IN THE RECOVERY BOILER

The analysis of technological processes for a real control object-a recovery boiler is performed in order to determine faults and possible emergency situations. The recovery boiler is considered as a complex control object (in which a chemical reactor is combined with a steam power boiler), which is advisable to decompose into several interconnected subsystems. The study was carried out in accordance with the HAZOP application manual in the form of a qualitative analysis of faults and possible abnormal situations in the recovery boiler. The study was conducted in accordance with the decomposition of the recovery boiler for each constituent of the interconnected subsystems. As a result of research, for each of the subsystems of the recovery boiler, HAZOP work tables were developed that allow you to identify root frames-linked to specific causes of possible faults.

MATHEMATICAL MODEL AND ALGORITHM FOR CALCULATION OF THERMAL STATE OF A REGENERATOR ACCUMULATING CONVERTER GAS HEAT OF COMBUSTION AND HEATING AIR FOR A RECOVERY BOILER

The heat of combustion of the converter gas, which is periodically formed in the oxygen-converter production at the metallurgical plant, is proposed to be used for alternate heating of the checkerwork of two regenerators (such as сowpers), and their alternate cooling by a continuous flow of air heated to a high temperature, and directed to the recovery boiler to generate steam. A mathematical model is presented that allows evaluating the thermal state of the regenerator, the temperatures of the heating gases and the heated air in the modes of heating and cooling the regenerator checkerwork. An algorithm for numerical calculation of the temperature fields of the regenerator checkerwork, gases and air is presented.