Steam Pipelines Research Articles

Optimization of the multi-level steam production and supply in industrial parks

Steam is an important medium for energy transmission in industrial parks. For providing steam to multiple users, it is key to determine the optimal number of steam levels in the design of steam system. With the increasing number of steam levels, the energy demand and supply can be better matched but the investment of steam pipeline network increases. In this paper, this trade-off is solved by a two-stage method. In the first step, a mixed-integer nonlinear programming (MINLP) model is established to minimize the total cost of the steam system of the industrial park, while a simple pipeline network optimization model is involved. The optimal scheme of steam production including the number of steam levels can be obtained automatically. In the second step, GeoSteiner algorithm is used for solving Rectilinear Steiner Minimum Tree (RSMT) model to further optimize the pipeline network separately. In a case study, the optimal number of steam levels is 3. The total annual cost (TAC) of the optimal steam system is 11.4%, 5.28%, and 1.43% lower than the schemes with the lowest pipeline network cost (1 level of steam), the best matching between heat supply and heat demand (6 levels of steam), and the largest electricity generation capacity (4 levels of steam), respectively. The sensitivity analysis indicates that the overall heat load required by consumers and the distance between the energy station and consumers can make a difference to the optimal number of steam levels.

Substantiation of the critical structural and mechanical state of low-alloy heat-resistant steel from steam pipelines of thermal power plant

The paper discusses metallographic studies and the results of mechanical testing of 15Kh1M1F (DIN 15CrMoV5-10) steel in the initial state and after its long-term operation in the steam pipeline of TPP. The revealed adverse impact of shutdowns of TPP units on the structural and mechanical state of steel is associated with the occurrence of cyclic thermal stresses in the pipe walls. Structural changes in metal across the pipe wall are uneven and consistent with regularities of mechanical properties changes. Intergranular fragments detected on the background typical transgranular relief of specimen’s fracture surfaces are considered fractographic signs of steel’s degradation. The part of intergranular fracture in the unit area of the fracture surfaces is proposed as the quantitative indicator of the changes in the structural and mechanical state of 15Kh1M1F steel due to its degradation. The critical state of steel is substantiated based on the regularities of operational changes in its mechanical properties and the revealed fractographic features.

Research and Application of the Original Position Statistical Distribution Analysis Method for Non-Metallic Inclusions in P91 Steel

Heat-resistant P91 martensitic steel is used to produce high-temperature steam pipelines in (ultra) critical power plants. However, non-metallic inclusions are inevitably produced in the metallurgical process. The type, composition, morphology, quantities, size and distribution of these inclusions have significant influences on the properties of materials. The present work developed an original position statistical distribution analysis method to characterize non-metallic inclusions in P91 steel based on scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS). Two samples from P91 steel pipes fabricated by different processes were examined. The non-metallic inclusions in these samples could be divided into spherical oxides, strand-shaped oxides, spherical sulfides, spherical oxygen–sulfur compounds, strip sulfides and other inclusions. The amount, proportional area, particle sizes, original positions and statistical distribution results of non-metallic inclusions in different processed samples were assessed, and the causes and effects of these inclusions were analyzed. This novel method could provide diversified information on inclusions, which is helpful for the improvement of metallurgical processes and service performance evaluations.

Use of Electrolytic Hydrogenation to Visualize the Damage of Long-Term Operated Heat-Resistant Steel of TPP Steam Pipelines

Use of Electrolytic Hydrogenation to Visualize the Damage of Long-Term Operated Heat-Resistant Steel of TPP Steam Pipelines

Creep Pores in Welded Joints of Steam Pipelines

Creep Pores in Welded Joints of Steam Pipelines

Study on the Influence of Coil Placement on Pulsed Eddy Current Testing

The pipeline system of plant is installed with an insulation layer on the outer wall of the pipeline. Currently, the primary methods of detecting pipeline system is ultrasound and uradiographic testing, which require the removal of the outside layer before testing. As a result, detecting time extends, and labor costs increase, increase the risk of accidental exposure. Applying the PEC technique for steam pipelines can eliminate the disassembly of insulation and achieve non-stop online screening. The defects testing by coil placement is an essential indicator of the PEC technique, which is the main influence factor of PEC accuracy. The article intensifies the modeling and simulation of the pipelines by applying Ansys Maxwell and designs coaxial and vertical detection coils to simulate the detection capability of PEC on flat bottom defects in case of consistency in the lift-off distance, materials, and other conditions. It selects nuclear power plant sample pipes for coaxial and vertical PEC testing. Recording the test result of PEC and UT methods, and the effects of two coil placement methods on PECT are compared. Finally, the study proposes development trends.

Influence of heat input on hot cracking sensitivity of the EA395-9 filler metal

Abstract Microcracks are always present in the deposited metal of 10MnNi2MoVA steel weld seam, which affects the safety of the power plant steam pipeline. It is important to investigate the effect of heat input on the hot cracking sensitivity of the EA395-9 weld metal. In this work, the deposition of the weld metal of EA395-9 was prepared, then the hot cracking tendency of the weld with the different heat input was analyzed and observed. The results show that the moderate welding heat input can help to avoid hot cracking.

Prediction of the Residual Creep Life of SA335-P22 Steel Main Steam Pipelines

In this study, the comprehensive properties of a P22 high-temperature steam pipeline with moderate spheroidization were evaluated after more than 11,700 h of operation through a series of physico-chemical properties testing, especially for a creep test. The remaining life of the P22 high-temperature steam pipeline was analyzed and predicted by the θ parameter method, to guide the normal operation of the P22 high-temperature steam pipeline.

Контроль и поддержание параметров эффективного функционирования паровой завесы трубчатой печи

Purpose. A review of the structure of a modern automated process control system of an oil refining complex allowed the authors to identify the lack of technical means for remote control of the effective functioning of a protective steam curtain of tube furnaces. Numerical simulation of changes in steam pressure in a steam pipeline at the site of a diesel fuel hydrotreating unit depending on the steam mass flow was carried out. Based on the results of the review and simulation, technical solutions were developed that provide remote control of steam pressure, as well as automatic maintenance of the set steam pressure parameters for the effective operation of a protective steam curtain of a tube furnace of a diesel fuel hydrotreating unit. METHODS. To obtain the results, the authors used general scientific and special methods of scientific knowledge such as analysis, synthesis and generalization, which are based on the provisions of systems and information theories. FINDINGS. The results of numerical simulation of changes in steam pressure in a steam pipeline at the site of a diesel fuel hydrotreating unit depending on the steam mass flow were obtained. It was determined that with the simultaneous launch of protective steam curtains of five tube furnaces, it is possible to reduce the steam pressure values below the normative ones. RESEARCH APPLICATION FIELD. The obtained results of the research can be used in tube furnace protective steam curtain systems at oil refineries and petrochemical plants to automate the control of steam pressure parameters and automatically maintain the set parameters of steam pressure when the values drop below the set ones. CONCLUSIONS. Based on the results of numerical simulation of changes in steam pressure in the steam pipeline at the section of a diesel fuel hydrotreating unit, depending on the steam mass flow, technical solutions were developed that provide remote control of steam pressure, as well as automatic maintenance of the set steam pressure parameters for the effective operation of the protective steam curtain of a tube furnace of a diesel fuel hydrotreating unit. Directions for further research are defined.

Development of preliminary design of the energy system of the Ningdong, Ningxia thermal power plant

The purpose of this design is to master the basic steps, calculation methods, and equipment selection methods of the thermal power system of the thermal power plant, and to familiarize with the composition, connection, and operation characteristics of the thermal power system through the preliminary design of 600MW thermal power plant thermal power plant. This paper is divided into five parts, selecting the principle thermal system formulation, calculating the principle thermal system, the selection of unit auxiliary equipment, steam pipeline calculation, and selection after and after successful calibration. The preliminary design of the thermal system is completed by drawing the comprehensive thermal system diagram and the local system diagram using the above calculation data.

Root cause of embrittlement of in-service exposed high pressure steam pipeline

A segment of tube cut off from the high pressure steam pipeline was subjected to routine basic material tests, which resulted in very low impact energy of the pipe material (low-alloyed Cr steel). A part of the segment (and a comparative non-operated sample) was then subjected to detailed mechanical tests (including creep), metallographic investigations and fractographic analyses with an aim to determine a root cause of the embrittlement. The results showed that grain boundaries of exposed steel are covered by particles of primary and secondary cementite. However, a matrix is weakened more, therefore a fracture of creep, tensile and impact specimens is always transgranular and the cleavage facets are limited to grain size, if present. Thus, the cause of embrittlement was determined not by a rapid ageing, but by an unsuitable initial heat treatment of the pipe material.

Two-parameter method for identification and location of leaks based on weak FBG for steam pipelines

In this paper, an online steam pipeline leakage monitoring method, based on a weak-reflectivity optical fiber Bragg grating (wFBG) array for temperature–vibration hybrid sensing, is presented. This method meets the requirements of long-distance, large capacity, low false positive rate (FPR), and low false negative rate (FNR). The drawing tower online-writing FBG technology was used to write the wFBG (−40 dB), which has the advantages of high strength and good consistency. A large-capacity sensor network is realized using mixed time-division multiplexing and wavelength-division multiplexing technology. A novel temperature–vibration composite optical cable structure was designed to realize multi-parameter pipeline leakage monitoring. A chirped wFBG array with a spatial resolution of 3 m and a narrowband wFBG array with a spatial resolution of 1 m were combined in the same optical cable to simultaneously monitor the vibration and temperature of the pipeline. Leakage of the steam pipeline is accompanied by changes in the temperature and vibration signals. The leakage and its location can be identified more accurately by changes in these two parameters in the wFBG wavelength and interferometric phase. The field experiment results show that this temperature–vibration two-parameter detection system can accurately identify and locate steam pipeline leaks and reduce the FPR. This validates the feasibility of the wFBG array-based temperature–vibration hybrid sensing technology for monitoring steam pipeline leakage.

Experimental determination of the heat exchange coefficient of industrial steam pipelines

The article discusses and analyses the factors related to the use of a thermal imaging camera to determine heat loss in industrial steam pipelines at factories from chemical and metallurgical industry, by measuring their surface temperature. The generally accepted enthalpy method for determination of the loss has serious drawback it gives accurate results, but in averaged units in which it is impossible to take account of the contribution of the different parts and components of the pipeline in the total heat loss. The unavailability of information on where, how and in what way along the route this loss is formed does not allow prompt and specific measures to be taken for its reduction. An attempt has been made to structure empirically a reliable analytic dependence for determination of the heat exchange coefficient, bringing together the various factors influencing the heat exchange. By the method of the least squares the free coefficient and the exponent have been determined of criterion equation satisfying initial and boundary conditions of the experiment. Based on the obtained results for determining the heat losses by measuring the surface temperature of steam pipelines with a thermal imaging system, a reliable and acceptable method is proposed, which has a place in engineering practice. For this purpose, an industrial experiment has been carried out at three actually operating steam pipelines of different diameters and steam parameters. A criterion equation has been derived that can be used as a mathematical model for software products with a practical orientation for regular assessment of heat losses of steam pipelines. Values of heat losses determined through energy balance of heat carrier and heat flux from the outer surface of the steam pipelines have been compared. Results for the heat exchange coefficient, obtained through a balance have been compared with the analytically determined values based on current standards. A new method has been developed for express evaluations of the current heat losses of the steam pipeline in real time, as the sum of the losses through its individual components gives as average values 9÷12 % increased results for the losses compared to the enthalpy method. Its great advantage is that it can be used selectively to determine the losses through individual sections of the steam pipeline.

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.

Determining the Factors Causing Resonant Vibrations in Main Steam Pipelines of Novovoronezh NPP-2 Unit 1

Determining the Factors Causing Resonant Vibrations in Main Steam Pipelines of Novovoronezh NPP-2 Unit 1

The Coal Dust Combustion Scheme for an Invert Furnace of an A-USC M-Shaped Boiler

The M-shaped boiler construction for the advanced ultrasupercritical steam parameters (A-USC) is proposed in this work. The boiler was designed to operate in a 500 MW unit on low volatile hard coal. This design allows reducing the pipelines length of the high cost steam pipelines made of nickel alloys. A downstream (invert) furnace is offered for this boiler type. The coal dust burning scheme design using the direct-flow burners and nozzles in a system of vertical and horizontal tangential torches and the solid ash removal are proposed. This approach was extensively used earlier on standard shaped boilers, and it was upgraded now for an invert furnace. The goals are achieved by conducting research on the physical furnace model and thermal furnace processes numerical simulation by computational fluid dynamics software. The most significant research results were as follows: the oxidizer stage supply was performed along the torch length and furnace height; the dynamic jet pressure on the furnace walls was excluded; a high degree of coal burnout was ensured due to the vortex furnace aerodynamics implementation; the uniform furnace section filling with air jets was performed; turbulent jets ejection was significantly higher than that for a flat submerged jet; chemical underburning loss did not exceed 0.1%; and unburned carbon loss was 0.8%. The carbon monoxide concentration at the furnace outlet in terms of air excess ratio equal to α=1.4 was 226 mg/nm3 . The nitrogen oxides concentration in the flue gases (normalized) was 424 mg/nm3 . The results significance obtained during the research is efficient solid fuel use with high technical and economic boiler performance.

Research and Development of Hybrid Power Units Heat Flow Diagrams with Cooled High-Temperature Steam Turbines

Fossil fuel thermal power plants account for almost 60% of Russian electricity and heat. Steam turbine units make almost 80% of this amount. The main method for steam turbine unit efficiency improvement is the increase in the initial steam parameters’ temperature and pressure. This reduces fossil fuel consumption and harmful emissions but requires the application of heat-resistant steel. The improvement in steel’s heat resistance leads to a non-linear price increase, and the larger the temperature increase, the more the steel costs. One of the methods of improving efficiency without a significant increase in the capital cost of equipment is an external combustion chamber. These allow an increase in the steam temperature outside the boiler without the need to use heat-resistant alloys for boiler superheaters and steam pipelines between the boiler and the steam turbine. The most promising is hydrogen–oxygen combustion chambers, which produce steam with high purity and parameters. To reduce the cost of high-temperature steam turbines, it is possible to use a cooling system with the supply of a steam coolant to the most thermally stressed elements. According to the calculations, the efficiency reduction of a power unit due to the turbine cooling is 0.6–1.27%. The steam superheating up to 720 °C in external combustion chambers instead of a boiler unit improves the unit efficiency by 0.27%. At the initial steam temperatures of 800 °C, 850 °C, and 900 °C, the unit efficiency reduction caused by cooling is 4.09–5.68%, 7.47–9.73%, and 8.28–10.04%, respectively.

Technological Solutions in the Field of Production and Use of Hydrogen Fuel to Increase the Thermal Efficiency of Steam Turbine TPPs

The paper discusses technological solutions in the field of production and use of hydrogen fuel, the combustion of which, in a steam-oxygen environment, can significantly increase the initial parameters of the steam turbine cycle and, thus, increase the thermal efficiency of traditional steam turbine thermal power plants. A study of technologies for the industrial production of hydrogen has been carried out. An analysis of the technical and economic features of hydrogen production technologies for use in the electric power industry showed that the most promising method is electrolysis, which makes it possible to obtain inexpensive hydrogen during hours of low demand for electricity or cogeneration of heat and electricity when electricity is a by-product. It is shown that in order to increase the power and efficiency of steam turbine TPPs, it is important to use external steam superheating from an external source of thermal energy, thus providing intermediate overheating of the working fluid by connecting an additional cycle with a higher equivalent initial temperature to the main steam turbine cycle. We have established that if we use hydrogen as a thermal energy source, the absolute efficiency of the steam turbine cycle can be increased up to 54%, taking into account the regenerative heating of feed water. In this case, at an overheating temperature equal to tnn = 760 °C, the absolute efficiency of the cycle is virtually equal to that of a CCGT unit operating at the initial gas temperature t0 = 1350 °C. At the same time, while maintaining the boiler performance, the rated capacity of the steam turbine power unit is increased by 12%. In addition, the study pays attention to the problem of increasing the power consumption of TPPs for the auxiliaries, as required to compress hydrogen and oxygen up to a pressure higher than that in the steam pipeline where the combustion chamber is installed. Our calculations have allowed us to conclude that, for the case of installing the combustion chamber in live steam, the share of additional power spent for auxiliaries should be 7%, whereas the main share of power is consumed for compressing hydrogen—94%. Despite the identified shortcomings, an economic analysis of the process of hydrogen production at TPP by electrolysis and its further use for intermediate overheating in steam turbines in order to increase their efficiency showed the effectiveness of this solution.

Влияние режимов работы заводских ТЭЦ на статическую устойчивость турбогенераторов при отделении от энергосистемы

The main trend of the electric power industry is the expansion of its own power supply sources of the industrial enterprises. At the same time, isolated operation mode remains the mode that may cause emergency conditions. The relevance of the conducted studies is confirmed by experience. Thermal power plants (TPP) are continuously reconstructed, the power of the generators is increasing, and they are transferred to operate in generator – transformer units. The generating equipment is constantly changing because of repairing, maintenance, and emergency conditions. Therefore, part of the machines operates in electrical mode, the other part operates in thermal mode. In case of isolated operation, some machines are unable to control frequency of the unit. Then, a danger of loss of static stability may occur under conditions of reactive power deficiency. In this regard, the research to define the reasons of the loss of static stability of industrial STG, to conduct computational experiments and to develop activities to reduce emergency situations is relevant. Calculation of the operating modes of industrial thermal power plant has been carried out using the KATRAN software package. A consistent weighting method is used to analyze the static stability of the power plant. The consistent equivalent method is applied to calculate the steady-state modes in case of isolated and parallel operation with the power system. An algorithm has been developed that differs from the existing ones as it considers the impact of the thermal load on the static stability factor of turbogenerators of industrial thermal power plants. Also, it allows you to choose turbine–generator unit that will maintain constant pressure in the steam pipeline. The modes of isolated operation have been studied in terms of static stability of the power plant when all speed control units are operating and in case that one of the turbine-generator unit operates to maintain constant pressure in the steam pipeline. The results have shown that during maintenance operation of one of the machines of thermal load can lead to loss of static stability. Recommendations to improve stability are presented. The obtained algorithm allows us to develop activities to increase static sustainability in case of isolated operation with the power system. The suggested key activity is to redistribute between the turbines the function to keep the steam pressure in the steam pipeline. The computational experiment conducted using the example of the industrial thermal power plant has proved its effectiveness.

Creep Damage in Steam Pipelines and the Use of Metallography in Verifying the Possibilities of Testing

With high operating parameters of the medium in medium-pressure and high-pressure steam pipelines of fossil power plants, creep damage occurs, especially in welded joints leading to complete rupture of the pipe wall in the last phase. Detection of creep damage at an early stage before major cracks may occur can prevent these accidents. For these purposes, phased array ultrasonic testing was performed using a high frequency probe. This testing was performed on real welded joints cut from the power plant. To verify the possibility of detection, metallographic analysis on the tested locations was performed. When comparing the results, it is possible to refine the interpretation of the ultrasonic data and the metallographic results can also be used in the eventual qualification of non-destructive testing.