Online monitoring supports plant reliability and performance management by providing real time information about the condition of equipment. However, the intricate geometries and harsh operating environment of coal fired power plant boilers inhibit the ability to do online measurements of all process related variables. A low-cost alternative lies in the possibility of using knowledge about boiler operation to extract information about its condition from standard online process measurements. This approach is evaluated with the aim of enhancing online condition monitoring of a boiler’s convective pass heat exchanger network by respectively using a soft sensor and a data-driven method. The soft sensor approach is based on a one-dimensional thermofluid process model which takes measurements as inputs and calculates unmeasured variables as outputs. The model is calibrated based on design information. The data-driven method is one developed specifically in this study to identify unique fault signatures in measurement data to detect and quantify changes in unmeasured variables. The fault signatures are initially constructed using the calibrated one-dimensional thermofluid process model. The benefits and limitations of these methods are compared at the hand of a case study boiler. The case study boiler has five convective heat exchanger stages, each composed of four separate legs. The data-driven method estimates the average conduction thermal resistance of individual heat exchanger legs and the flue gas temperature at the inlet to the convective pass. In addition to this, the soft sensor estimates the average fluid variables for individual legs throughout the convective pass and therefore provides information better suited for condition prognosis. The methods are tested using real plant measurements recorded during a period which contained load changes and on-load heat exchanger cleaning events. The cleaning event provides some basis for validating the results because the qualitative changes of some unmeasured monitored variables expected during this event are known. The relative changes detected by both methods are closely correlated. The data-driven method is computationally less expensive and easily implementable across different software platforms once the fault signatures have been obtained. Fault signatures are easily trainable once the model has been developed. The soft sensors require the continuous use of the modelling software and will therefore be subject to licencing constraints. Both methods offer the possibility to enhance the monitoring resolution of modern boilers without the need to install any additional measurements. Implementation of these monitoring frameworks can provide a simple and low-cost contribution to optimized boiler performance and reliability management.

Boiler feed pump turbines (BFPTs) are in use at a number of Eskom power stations. They utilise bled steam extracted from the main turbine in order to drive multistage centrifugal pumps which supply the boilers with feedwater. With an increase of renewables in the energy mix, the need for Eskom’s coal-fired power stations to run for extended periods at very low loads has arguably never been this great. Various systems affect the ability of these generation units to run economically at low loads. One such system is the boiler feed pump turbine and its associated pumps. A station was selected from Eskom’s fleet based on access to information and the station being a relatively typical plant. The Unit (a boiler and turbogenerator set) selected for study was one with the most thorough instrumentation available for remote monitoring. The BFPT system of this Unit was modelled in Flownex, a one-dimensional thermofluid process modelling package. The model included individual pump stages, steam admission valves and a stage-by-stage turbine model utilising custom stage components. These turbine stage components represent each stage with nozzles and other standard Flownex components. The boundary conditions of the system were set as functions of generator load in order to represent typical values for use in case studies. The relationships between load and boundary conditions were based on large samples of data from the station’s data capture system (DCS). A corresponding standby electric feed pump system was also modelled in Flownex for a comparative case study. After model validation, a number of case studies were performed, demonstrating the functionality of the model and also providing specific results of value to the station in question. These results include the minimum generator load possible with different steam supplies; maximum condenser back pressure before plant availability is affected; the viability of changing the pump leak-off philosophy; and the effect of electric feed pump use on power consumption. The main recommendations from the case studies were as follows: i. to stroke the steam admission valves as per the design charts, ii. to test the operation of the BFPT down to 40 % generator load, iii. to keep the pump leak-off philosophy unchanged, iv. to maintain the cooling water system and condensers sufficiently to avoid poor condenser vacuum, v. to reconsider the decommissioning of the “cold reheat” steam supply, vi. and, to favour use of the BFPT over the electric feed pumps at all generator loads.

The boiler flue gas furnace exit temperature (FET) is a key operating parameter of coal fired steam boilers. From the design perspective, the FET is vital for materials selection and sizing of heat transfer surfaces. From an operating perspective, it is a major indicator of the rate of combustion and heat transfer that is occurring within the furnace. Downstream of the furnace, the FET has a significant impact on both the performance and reliability of the boiler heat exchangers, which ultimately impacts on both boiler efficiency and availability. Monitoring of the FET can advise operating and engineering corrective actions which will ultimately result in better efficiency, reliability and availability together with the associated economic benefits. Therefore, methods of determining FET are investigated. Two methods are focused on for this study, one indirect and one direct. The indirect method studied is a mass and energy balance method which begins with a global boiler mass and energy balance to calculate the major boiler flow rates of coal, air and flue gas which are difficult to measure online. These parameters are then used as inputs into a furnace or backpass mass and energy balance to calculate the furnace exit temperature. The method is applied to a case study, and is evaluated in terms of the measurement uncertainties which are propagated on the intermediate parameters calculated, as well as on the final calculated FET. The main conclusions are that this indirect method contains various uncertainties, due to parameters which have to be assumed such as (i) the distribution of ingress air (also called tramp air) in the different sections of the boiler and (ii) the estimation of the share of water evaporation heat transfer occurring in the water walls of the furnace part of the boiler. The method is however still useful and can be easily applied to any boiler layout and can be used as a reference tool to verify other measurements. The direct method studied is acoustic pyrometry. The work specifically focuses on the sources of error in determining the temperature from the measurement of the time of flight of sound, the impact of particle concentration on the speed of sound through a gas-particle mixture, and the temperature profile reconstruction from acoustic time of flight measurements. A limited set of physical testing was also carried out using one acoustic generator and receiver to take measurements on a real coal power plant. As part of this physical testing, the detection of time of flight from acoustic signals was explored. Already installed radiation pyrometers were also used as a reference for interpreting the acoustic measurements. The indications are that the acoustic pyrometer provides a more representative temperature measurement than the radiation pyrometers. The uncertainty of the acoustic measurement for the same case study as the indirect method was determined and compared with the calculated result. While many aspects still need to be researched further, this initial study and experimental testing produced very promising results for future application of acoustic pyrometry for better monitoring of the coal combustion processes in power plant boilers.

This masters’ thesis deals with a thermal design of a draft dry bottom boiler for bituminous coal that should replace a disassembled boiler in a current boiler room. Application of SCR is intended in order to reach emission standards of NOx.

The main goal of this Master's thesis was to design heat recovery steam boiler for cogenera-tion unit of a biogas plant while flue gas was flowing from an engine exhaust. Its temperature and required pressure of a steam were assigned. The thesis contains thermal, aerodynamic, hyd-raulic calculations and verification of wall thicknesses for pressure parts of the boiler. Follow-up results of these calculations served for making of projection drawings as well as equipment needed for reliable boiler operation.

This thesis deals with the design of a co-combustion gas boiler for coal gas and blast furnace gas mixture. The calculation includes stoichiometry, determinination of the boiler efficiency, steam production rate and heating surfaces sizing. This thesis also includes technical documentation of designed gas boiler. The calculation of the boiler meets the values specified by the scripts and also by documentation from PBS. The boiler was designed for 113.9 MW and 93.77 % efficiency.

The diploma thesis deals with optimization of pellet boiler for agropellets combustion. On the Czech market are mostly available boilers for burning wood pellets. Specially adapted agropellet boilers are pretty expensive. The work is divided into two main parts. The first part contains a research of agropellets, agropellets production and combustions of agropellets. The second part is experimental and describes the combustion test. It describes the measurement procedure, the necessary calculations and evaluation.

This master thesis deals with the properties of digestate in combustion, design of construction solution of digestate boiler and experimental verification of boiler parameters. The first chapter deals with the properties of digestate as a fuel. It is followed by a chapter dealing with the existing measured results on a similar boiler. This is followed by a stoichiometric calculation of the digestate boiler. The next chapter is devoted to combustion chamber models. This chapter is followed by a chapter with experimental verification of chamber models and combustion process tuning. The last chapter contains design of construction and operational measures.

This thesis is focused on the application of advanced methods for evaluating damage to boiler tubes, specifically temperature related damage. The aim of this work is to develop an improved damage evaluation procedure utilizing capabilities of modern approaches. This work describes various types of industrial boiler damage. The main focus is on the most exposed and often the most damaged parts of boilers, which are tube bundles (for example, superheaters). Equipment damage is undesirable and often leads to leakages or even to the boiler shutting down. Therefore, it is necessary to find the problem as soon as possible and make the required changes to prevent further damage. The damage types are divided into five categories based on the damage mechanism. Temperature has one of the biggest influences on damage and it may cause short-term or long-term overheating in the tube bundles. This type of damage occurs when the designated temperature is exceeded and results in reduced creep life. It is necessary to know the real surface temperature history of the tube bundle to estimate temperature related damage, however this is often not available. Therefore, it is necessary to calculate those temperatures based on the available data (i.e. inlet and outlet temperatures and pressures). This is real challenge due to the combination of complex flows of the working substances (mainly flue gasses) and heat transfer. Considering available data, new approach is proposed in order to obtain information required for residual creep life estimation. In the first step, thermal – hydraulic calculation is performed followed by a thermal load estimation of a superheater tube bundle in a natural gas fired boiler, using CFD simulations. In the next step, the surface temperature is evaluated and used to determine the temperature related damage, specifically the creep life estimation. The life expectancy is in some ways influenced by imperfections, and therefore at the end of this thesis the influence of the oxide layer on the inner side of tube and fouling on outer side of tube is described.

The diploma thesis contains calculations of gasification of coal boiler. The first part of thesis contains stochiometric calculations, heat balance and calculations of combustion chamber. In the next part are calculations of heat exchange surfaces and at the end of this part are calculations of regenerative air heater and total boiler balance. Calculations are made by regard to investments costs, preservation of the steam parameters and keeps emissons limits.