Boiler Start-up Research Articles

Application of Non-Fuel Power Generation Technology in Steel Industry

Through continuous equipment technology transformation and full utilization of Ma Steel's abundant gas, the boiler no longer relies on fuel oil for stable combustion during boiler startup, sliding parameter shutdown, and RB, thus achieving safe and stable operation of the boiler under any abnormal working conditions, and achieving good economic and social benefits.

Simulation and experiment of plasma ignition of low-grade coal

A plasma-coal burner is studied utilizing a model of plasma thermochemical preparation of coal for combustion, implemented in the PlasmaKinTherm program. For boiler start-up and coal combustion stabilization, plasma-coal burners do not require fuel oil or gas. The PlasmaKinTherm program combines thermodynamics and kinetics to describe the thermochemical preparation of fuel in the plasma-coal burner volume. The purpose of the simulation was to determine the conditions for plasma ignition of low-grade coal. A numerical study was carried out of the influence of the plasmatron power on the ignition of the air mixture (coal + air). High-ash Ekibastuz coal was used in the calculations. The distributions of temperature and velocity of gas and coal particles and concentrations of products of plasma thermochemical preparation of coal for combustion along the length of the burner were calculated. As a result of the analysis of the processes of plasma ignition of coal, their main patterns were revealed, including the shift of the maximum temperatures and velocities of the products of thermochemical preparation of coal for combustion upstream (towards the plasma torch), as well as the fact that the maximum values of temperatures and velocities of the products do not depend on power plasmatron. At the plasmatron power determined by kinetic modeling, experiments were conducted to test and validate the ignition and combustion conditions for a highly reactive two-component fuel torch. The assumptions made during the development of the mathematical model were confirmed by comparing the calculations with experimental data.

Optimisation of the cooling of pressurised thick-walled components operating with fluid at saturation temperature

Determining the optimum heating or cooling times for thick-walled pressure elements allows a steam boiler to reduce start-up or shutdown times. A new method has been developed to determine the optimum fluid temperature change to shorten the steam boiler start-up and shutdown. The fluid temperature curve is designated so that the total circumferential stress at the hole edge does not exceed the allowable stress. The total stress at the hole edge where it is concentrated consists of thermal and pressure stress. The example of the optimum cooling of the steam boiler drum illustrated the method used. A three-dimensional finite element method (FEM) analysis was carried out for the connection between the drum and the downcomer to determine the transient temperature and stress distributions. It was shown that the total circumferential stress due to pressure and thermal loading at the hole edge did not exceed the allowable stress when optimal fluid temperature changes were used. The method shown in this paper was compared with the boiler standard EN 12952-3, which permits the determination of allowable heating and cooling rates of boiler pressure components as a function of pressure. The comparison shows that the cooling/heating time determined by the new method can be significantly shorter than that determined by the method in EN 12952-3. By using the new method for designating the optimum fluid temperature, the flexibility of the boiler and the power unit can be improved as the heating or cooling of critical pressure elements can be more rapid. It can also be used to accidently cool PWRs (Pressurised Water Reactors) and BWRs (Boiling Water Reactors) pressure vessels.

Dynamic characteristics of pollutant emissions from CFB boilers during periodic fire banking and start-up

It is difficult to control pollutant emissions during fire banking and start-up in CFB boilers, which poses threats to power plant operation, safety and environmental protection. A 350 MW supercritical CFB boiler was taken as the research object. Using the CPFD method and Barracuda software, a full-loop combustion and pollutant emission model was constructed to simulate periodic fire banking and start-up, and the gassolid flow characteristics and pollutant emission characteristics were analysed. The results showed that the bed material at the bottom of the furnace exhibits obvious stratification after being stationary, and this stratification has an impact on the generation, distribution and emission of NOx and SO2 in the furnace. Eighty-five percent of the bottom bed material is lower layer, and the NOx and SO2 concentrations are negatively correlated with the volume fraction of particles. The average NOx and SO2 concentrations in the lower layer are 120.05 mg/m3 and 1155.50 mg/m3, respectively. During the hot start-up process, the NOx concentration decreases with increasing bed height. The residence time of the desulfurization reaction is prolonged, the desulfurization efficiency is improved, and the SO2 concentration is reduced. These results provide a theoretical basis and a certain reference value for the periodic fire banking and start-up of supercritical CFB boilers.

Analysis of Ignition Characteristics and Influencing Factors of Combustible Fly Ash in Boiler Start-Up Stage Flue Gas

In order to realize the full-time denitration of a boiler, high-temperature flue gas needs to be introduced when SCR is conducted during the boiler start-up stage, and there is a fire risk due to the presence of combustible fly ash at this time. Therefore, research on reburning and the explosion risk of tail flue gas encountering high-temperature flue gas during start-up and shutdown was carried out. A small testbed was designed to record the temperature of the flue gas and the composition of the flue gas before and after the test, and the ignition characteristics of combustible fly ash in the flue gas were systematically studied. The ignition temperature of combustible fly ash in various conditions was obtained, the ignition characteristics of combustible fly ash in the airflow were analyzed, and the effects of combustible gas, high-temperature flue gas temperature, and fly ash composition on ignition were also analyzed. The results show that the flue gas temperature in the test section was about 400 °C, the low-temperature flue gas temperature increased from 650 °C to 813 °C, and the combustible fly ash did not ignite regardless of whether alcohol was added as a combustible gas component. When the volatile content of combustible fly ash was 10~26.7%, the ignition temperature was 660~760 °C. The lower the volatile content of combustible fly ash was, the higher the ignition point was. When alcohol was added as a combustible component of gas, the ignition point decreased by about 50 °C. The critical ignition temperature of combustible fly ash in this test was lower than that under actual power plant operation conditions.

Ignition and combustion of a group of waste-derived fuel slurry droplets: Mutual influence upon low-temperature convective heating

Waste-derived slurries can be burned both in a fluidized bed and when injected into a boiler furnace. This paper is the first to analyze the dynamic characteristics of ignition and combustion of a group of three slurry droplets based on coal slime, water, and waste industrial oil in a low-temperature air flow with a temperature of 500–600 °C and velocity of 0.1–1.2 m/s. The distance between the droplet centers varied from 3 to 15 mm. The results of the study can develop innovative technologies for flare and fluidized bed combustion of fuel slurries at the boiler start-up stage. It was found that a distance of 3–5 mm between droplet centers provides almost simultaneous gas-phase ignition of all droplets. A further increase in the distance critically worsened the ignition and combustion and eliminated the synergy. An increase in the air flow velocity contributed to the appearance of a common flame zone but at the same time increased the ignition delay of droplets by a factor of 1.2–1.6. The negative effects of cooling and entrainment of combustion products by a low-temperature flow can be effectively reduced by adding 5 wt% of industrial oil to the slurry. Also, the use of oil reduced the droplet ignition delay time by 15–20%. At the stages of flame and heterogeneous combustion, the differences for droplets in a group increased (the stage durations differed by 1.5–3 times). For the low-temperature start-up of a boiler, it was found advisable to provide a droplet flow with a sufficient density to stabilize their ignition without significant flow deviations (dimensionless distance 1.5–2.5).

Design of diffuser (reducing stage assembly) for superheater and reheater start up vent silencer in super critical once through boilers

In supercritical boiler Startup Vent diffuser is to manage the instant release of huge amounts high pressure of steam to low pressure into atmosphere while cutting of the noise produced while venting the steam in different temperature and pressure conditions. The upstream pressure of startup vent is around 81 kg/sq.cm. so for reducing pressure from 81 kg/cm2 to 3kg/cm2 with constant flow one diffusers (reducing stage assy.) will introduce which will diffuse the pressure. Startup Vent diffuser is a design a reducing stage assembly (called a multistage diffuser) along with study of hydrodynamic parameter like Beta ratio, Mach number, and numerical calculation of orifice plate thickness, size of orifice hole & Bending stress evaluation, reducer etc.

Simulation of the Troitsk District Power Plant 660-MW Power Unit Boiler Startup Modes without Using the Startup Circulation Pump or Estimation of the Boiler Lower and Upper Radiant Parts’ Temperature Operating Conditions

Simulation of the Troitsk District Power Plant 660-MW Power Unit Boiler Startup Modes without Using the Startup Circulation Pump or Estimation of the Boiler Lower and Upper Radiant Parts’ Temperature Operating Conditions

Analysis of Boiler Start-Up Failure Risk with Grey FMEA and RCA Methods in Pt. PLTU Nagan Raya

PT. PLN (Persero) UPK Nagan Raya is a Steam Power Plant (PLTU) that uses coal as Boiler fuel to produce thermal energy. one of the initial stages of the Boiler is Startup as the basis for the start of Boiler operations. The purpose of this study is to analyze and avoid the risks that can make the operating system not run. Based on the research conducted, there are 8 risks that can cause failure. Based on the Grey FMEA method, the priority risk that occurs is that the FO fast shut-off cannot be O / C CCR with a value of 0.491 and also in the flexible joint line of the lower burner air there is a leak of 0.503. The result of the Root Cause Analysis method, the cause of the FO fast shut-off cannot be O / C CCR is the limited facilities and infrastructure for device maintenance which causes obstacles for workers so that the results worked on are not effective and efficient. Meanwhile, the risk that the flexible joint line air lower burner has a leak because it is not critical equipment only used at certain times so the check is neglected which makes the flexible joint leak. The solution that can be done is that as much as possible the operator must carry out routine maintenance/overhaul on the flexible joint so that there is no failure that can hinder the operation.

Identification of Transient Steam Temperature at the Inlet of the Pipeline Based on the Measured Steam Temperature at the Pipeline Outlet

A solution to the inverse heat transfer problem (IHP) occurring in steam pipelines is presented in the paper. The transient steam temperature at the pipeline inlet was determined from the steam temperature measured at the pipeline outlet. Temporary changes of steam temperature at the turbine inlet are set by the turbine manufacturer and result from the conditions of safe starting of the turbine and maintaining high durability of its components. The boiler start-up should be carried out so that the time-temperature changes at the boiler outlet equal the time-temperature changes determined using the inverse problem. In this paper, the inverse problem of heat transfer in the pipeline was solved by the finite volume method using data smoothing, future times steps, and Tikhonov regularization that stabilized the solution of the inverse problem. The determined transient steam temperature at the pipeline inlet was compared with the measured temperatures. The steam temperature at the inlet to the pipeline, which is the solution to the inverse problem, agrees very well with the measured temperature, as the absolute value of the relative difference εT between measured and calculated temperature is between 0.045% and 0.3%, and the root mean square error RMSE is within the range of 0.038 K to 0.322 K.

Impregnation of different coals and biomass with rapeseed oil for intensifying their ignition in a heated air stream during oil-free boiler start-up

Studies were conducted to develop the scientific basis for the use of low-grade solid hydrocarbons and biomass as starting fuel and an energy additive to the main fuel for coal-fired boilers. Char, softwood sawdust, brown and bituminous coals with a particle size of 140–250 μm were used in an air-dry state and after impregnation with rapeseed oil. Analytical studies included surface texture analysis of solid fuel particles, determination of their wetting properties with respect to water and rapeseed oil, thermogravimetric and calorimetric analyses, FTIR analysis of gaseous combustion products, analysis of the elemental composition and texture of the ash surface. Fuel combustion characteristics were studied in conditions of fine fuel particles movement in a heated air stream: 5 m/s, 500–800 °C. Impregnation of solid fuels with oil led to the moisture displacement from the pores of fine particles (oil content in various solid fuels 5.6–22.4%). It increased the combustion completeness of fine particles in a shorter period of time (the ignition delay time reduced by 15–30%) and the thermal effect of the exothermic reaction (by 2.2–18.1%). Oil vapors first ignited in the vicinity of the particle, thereby intensifying the combustion of solid component in fossil fuels.

Thermal and flow calculations of platen superheater in large scale CFB boiler

Circulating Fluidized Bed (CFB) boilers are desirable technology to utilize solid fuels, operate within a wide load range, and promote the high flexibility in burning a wide range of coal and other solid fuels, keeping high efficiency and low gaseous pollution. The paper presents thermal and flow modeling results of steam superheater operated in the large-scale coal-fired CFB boiler, both in steady and transient states. The mathematical model of the superheater wall was developed using Control Volume-based Finite Element Method. The heat transfer coefficient as the sum of radiative and convective heat transfer coefficients was considered in the presented approach to modeling thermal processes in a circulating fluidized bed. The overall heat transfer coefficient was computed for the analyzed type of the boiler at full load and steady-state conditions using available measuring data and results obtained using Computational Fluid Dynamics (CFD) modeling. Depending on the modeling approach adopted in the CFD model, the heat transfer coefficient at full boiler load varies between 159.96 and 189.63 W/(m2·K). In the analyzed period of boiler start-up, results of steam outlet temperature (455 °C–485 °C), heat transfer coefficients on the flue-gas side (100 W/(m2∙K) and 120 W/(m2∙K)), and heat transfer coefficients on the steam-side (925–2008 W/(m2∙K)) vary with time. The methods presented in the paper can be applied to modeling transient flow and thermal processes in superheaters with complicated flow arrangements. The advantage of the proposed method is a short computing time compared to detailed and complex 3D models. The developed model of the superheater with the transfer coefficient determination methods can be used to perform calculations in the full range of boiler load, both during steady and transient boiler operation.

Increase the flexibility of steam boilers by optimisation of critical pressure component heating

The paper presents a new method for determining the optimum fluid temperature changes during heating cylindrical thick-walled components weakened by holes. An inverse heat conduction problem was solved to determine the temperature of the fluid so that the equivalent total stress due to pressure and thermal load at the edge of the hole at the point of concentration does not exceed the allowable stress. The stress concentration factor at the edge of the hole was determined using the Finite Element Method (FEM) to represent the actual shape of the junction between the element and the stub. Optimum temperature changes of the steam-water mixture in the boiler drum and live steam temperature in the outlet header of the final superheater during the boiler start-up were determined. Based on the optimum time temperature and pressure variations determined for all boiler pressure elements, it is possible to identify the critical element. The heating time for the critical element is the longest. The critical boiler element governs the process of boiler start-up. The flexibility of the boiler can be significantly improved using the proposed method as boiler start-up times can be shortened by approximately one-third compared to current practice.

Application of adjacent heating technology in thermal power unit

There are many problems in the start-up stage of thermal power unit, which seriously affect the safe and economic operation of the unit. Therefore, it is of great significance to study the energy-saving technology of thermal power unit in the start-up stage. The adjacent heating technology is put forward to solve these problems in the boiler start-up stage. Thermal power unit USES the adjacent machine heating technology, improve the conditions of the boiler ignition and steady combustion conditions, improve the safety of the boiler start-up, saves the costs of fuel oil, coal, electricity, strengthened the flushing efficiency, shorten the flush time, improve the economic benefit of the adjacent machine, and prevent the scale caused by dramatic change wall temperature fall off, It can also ensure the safe operation of desulfurization, denitration and dust removal devices, and reduce the emission of pollutants, so it has a broad application prospect.

An experimental investigation into the fuel oil-free start-up of a coal-fired boiler by the main solid fossil fuel with additives of brown coal, biomass and charcoal for ignition enhancement

The research is focused on the ignition of solid fuels in a heated air flow. The experimental conditions correspond closely to solid fuel combustion in coal-fired boiler furnaces. Charcoal, wood, brown and bituminous coals were used as independent solid fuels and as fuel mixture components. The particle sizes of these fuels were less than 40 μm, 40–140 μm, 140–250 μm, 250–375 μm and 375–800 μm. They were ignited under the conditions of radiant-convective heating as they were moving in a heated air flow with a temperature of 500–800 °C and at a velocity of 5 m/s. The ignition delay time was the main investigated characteristic, recorded by a high-speed video camera. The induction period of bituminous coal shortens by 25–35% when 25–50% brown coal or wood in an air-dry state is added. The lowest ignition delay times were established for the fuel mixtures of bituminous coal with dry charcoal. The experimental curves of the ignition delay times of fuels and their mixtures versus the heated air temperature were presented as approximation equations. Based on the conducted research findings, a muffle burner design with a vortex structure of the fuel-air flow was proposed for the fuel oil-free start-up of coal-fired boilers.

Optimisation of heating and cooling of pressure thick-walled components operating in the saturated steam area

The paper presents a new method of determining optimum temperature variations of the fluid during heating and cooling of cylindrical thick-walled components weakened by holes. The temperature of the fluid located or flowing through the pressure component is equal to the saturation temperature.The stress concentration factors at the edges of the holes were determined using the Finite Element Method (FEM) to represent the real construction of the junction between the element and the spigot.Optimum fluid temperature variations were determined so that the maximum equivalent stress at the edge of the opening is equal to the permissible stress determined concerning thermal fatigue. The equivalent stress at the hole edge at the point of its concentration includes thermal stress and stress due to pressure. Optimum temperature changes of hot water and steam-water mixture were determined during heating up and cooling down of the boiler drum, i.e., during boiler start-up and shutdown.Three-dimensional computations of the transient field of temperature and stress were carried out for the junction of the drum and downcomer to show that the equivalent stress at the edge of the hole does not exceed the allowable stress if the optimum temperature of the fluid was estimated by the proposed method.

Selecting optimal conditions for the turbine warm and hot start-up

The paper discusses optimization issues related to start-ups from intermediate states defined as hot and warm, i.e. start-ups carried out after a few or several hours of downtime. Such start-ups are characterized by a non-uniform field of the initial temperature. For this reason, any simulation of start-up processes should be preceded by simulations of the cooling process to obtain a close-to-real temperature distribution at the moment when the start-up process is to begin. This is of particular importance in the case of elements in contact with the outer environment, such as outer casings and rotors. The simulation results indicate that it is possible to speed up the start-up procedure as recommended by the turbine manufacturer without exceeding allowable stresses in the turbine elements. Naturally, this will have a beneficial impact on the flexibility of the power unit operation. Rotors are characterized by the most difficult operating conditions and it is for them directly that start-ups should be optimized. The maximum start-up rate is determined by the initial temperature field of the turbine element material. For this reason, the paper presents a concept of initial heating of the turbine key elements. Running the process during the boiler heating and start-up might substantially shorten the total time needed to restore the power unit operation. Instead of sequential heating, the boiler heating and the turbine heating processes could be carried out in parallel.

Laboratory and industrial studies of gas coal ignition and combustion using high-voltage alternative current plasmatron

This paper presents experimental studies and industrial applications of a promising method for igniting and combusting coal fuel using a high-voltage alternative current plasmatron. Experimental studies were carried out at a set-up with a thermal capacity of up to 5 MW. Kuznetsk long flame coal selected after a ball-drum mill with sieve residue R90 = 15%, was taken as an experimental sample. The first experimental data on implementation of the combustion process have been obtained. Introduction and first industrial tests of the high-voltage alternative current plasmatron were carried out using a real power boiler TP-10 with an output capacity of 220 tons of steam per hour with gas and fuel oil replacement by coal during the process of boiler start-up.

Experience of Developing Plasma-Assisted Boiler Startup and Flame Support Systems

The results of the participation of the All-Russia Thermal Engineering Institute in the implementation of systems for plasma-assisted startup of and flame stabilization in the boiler of the Cherepet’ TPP are discussed.

New method for determining the optimum fluid temperature when heating pressure thick-walled components with openings

A new approximate method of optimum heating cylindrical pressure elements weakened by openings was proposed. Optimum variations in fluid temperature when heating the pressure component were determined from the condition that the total circumferential stress at the edge of the opening, resulting from the thermal load and pressure is equal to the allowable stress. The allowable stress is determined from the Wöhler fatigue diagram for a given number of start-ups and shutdowns of a power unit from the cold state. Optimum temperature changes are difficult to estimate at the beginning of the heating, using both exact analytical and numerical methods. In case of analytical methods, this is due to the very slow convergence of a series for near-zero time in the exact solution. In this paper, the optimum temperature changes of the fluid at the beginning of heating were determined using the heat balance integral method (HBIM). This method makes it possible to determine with high accuracy the temperature of the fluid for times close to zero, i.e., at the beginning of the heating process. In the second stage of heating, the optimum fluid temperature was determined on the assumption of a quasi-steady temperature field in the pressure element. The problem analysed in the article is important to increase flexibility of boilers and steam units. By optimising the heating up of the boiler during boiler start-up, the start-up time of the boiler and the whole unit can be significantly shortened and the power unit can be quickly connected to the power system.