Tolerable Risk for Hydrogen Sulfide in Sewage Treatment Plant- STP

Hydrogen sulphide is a toxic gas, it can cause a range of physiological responses from simple annoyance to permanent injury and death. There are a number of approaches to deal with the impacts of toxic gases. This study focused on minimizing the hazard exposure for hydrogen sulfide in the different operational zones for activated sludge process in sewage waterplant. Research tools/ approaches conducted were interviews, toxic gas testers, analysis report interpretation & quantitative risk assessment method. The study was conducted on Arabian Peninsula during the period (September 2019- September 2021). The (13) operational locations tested for toxic gas concentrations were inlet chamber, outlet channel, coarse /fine screens, primary sedimentation tank, activated sludge tanks, secondary sedimentation tanks, gas desulfurization unit, disc filters, chlorine dosing unit, sludge dewatering, sludge silos and digester tanks. The study found that the highest concentration for H₂S in the inlet chamber/ outlet channel. The severity hazards in the sewage treatment plant using activated sludge process are the asphyxiation by H₂S was extremely high can cause harm to public health, followed by the radiation hazard followed by electrical hazard, then (working at height, mechanical, traffic, health, chemical, physical, ergonomic, environmental, microbial and natural). The frequency of hazards occurrence is asphyxiation by H₂S was extremely high followed by the radiation hazard and health hazard including the infection with Covid 19 virus followed by mechanical hazard then (electrical, traffic, ergonomic, natural, chemical, physical and natural). Control measures were recommended to minimize the risk of asphyxiation by H₂S in the working environment at the STP.

Strength and Service Life of a Steam Turbine Stop and Control Valve Body

The stability of operation of steam turbines depends (along with other factors) on the reliable operation of their steam distribution systems, which are based on stop and control valves. This paper considers the strength of the elements of the K-325-23.5 steam turbine valves, in whose bodies, after 30 thousand hours of operation, cracks came to be observed. Previously determined were the nature of gas-dynamic processes in the flow paths of the valves and the temperature state of the valve body in the main stationary modes of operation. To do this, a combined problem of steam flow and thermal conductivity in stop and control valves was solved in a three-dimensional formulation by the finite element method. Different positions of the valve elements were considered taking into account the filter sieve. The assessment of the thermal stress state of the valve body showed that the maximum stresses in different operating modes do not exceed the yield strength. Therefore, the assessment of the creep of the valve body material is important to determine the valve body damage and service life. Modeling the creep of the stop and control valves of the turbine was performed on the basis of three-dimensional models, using the theory of hardening, with the components of unstable and steady creep strains taken into account. The creep was determined at the maximum power of the turbine for all the stationary operating modes. The maximum calculated values of creep strains are concentrated in the valve body branch pipes before the control valves and in the steam inlet chamber, where in practice fatigue defects are observed. However, even for 300 thousand hours of operation of the turbine (with a conditional maximum power) in stationary modes, creep strains do not exceed admissible values. The damage and service life of the valve bodies were assessed by two methods developed at A. Pidhornyi Institute of Mechanical Engineering Problems of the NAS of Ukraine (2011), and I. Polzunov Scientific and Design Association on Research and Design of Power Equipment. (NPO CKTI) – 1986. The results of assessing the damage and the turbine valve body wear from the effects of cyclic loading and creep of the turbine in stationary modes for 40, 200 and 300 thousand hours show that the thermal conditions of the body in the steam inlet chamber are not violated (without taking into account possible body defects after manufacture). The damage in valve body branch pipes after 300 thousand hours of operation exceeds the admissible value, with account taken of the safety margin. At the same time, the damage from creep in stationary operating modes is about 70% of the total damage. The maximum values of damage are observed in the areas of the body where there are defects during the operation of the turbine steam distribution system. The difference between the results of both methods in relation to their average value is ~20%.

Numerical study of a double inlet chamber counter flow vortex tube with insulation

The present study intends to improve the performance of the Ranque-Hilsch counter flow vortex tube, analysed using computational fluid dynamics. In the axisymmetric 3-D, steady-state, compressible, and turbulent flow vortex tube, the air has been used as the working fluid. The ANSYS17.1 FLUENT software has been used with the standard º-ε turbulent model for different mass fraction of cold fluid and inlet pressure in the numerical simulation and validated with the experimental results. It is observed from the study that as the inlet chambers number increases from 1 to 2, there is a decrease of 7.8 % in the cold exit temperature of the vortex tube. However, insulating the double chamber vortex tube leads to a further reduction of 4.2% in the cold exit temperature. Therefore, it indicates that the overall decline in the cold exit temperature from one chamber non-insulated vortex tube to double chamber insulated vortex tube is 9.6%. In terms of cold exit temperature, it can be concluded that using a double inlet chamber vortex tube with insulation yields the optimum results.

Development of a Two-Chamber MHD Tundish for Metal Ca

Introduction. The multifunctional magnetodynamic tundish prototype is the first world magnetodynamic mixer and batcher for steel, which has a capacity of up to 10 tons of melt and an inductor electric power of 600 kW. Ithas been successfully introduced into industry. Further works aim at adapting this device to continuous casting, in particular at obtaining semi-continuous cast billets at metallurgical micro-plants.Problem Statement. Today, the study of the effect of electromagnetic field on melt stirring and removal of non-metallics in the inlet chamber of MD-T is an urgent task.Purpose. The purpose of this research is to substantiate and to create MD-T as a two-chamber aggregate additionally equipped with a few electromagnetic & MHD devices for different purposes, to be used at metallurgical micro-mills.Materials and Methods. Physical modelling has been applied for studying liquid metal stirring under the action of electromagnetic field and the removal of non-metallics.Results. The behavior of the liquid jet falling from the ladle into the centrifugal chamber has been studied. The influence of the rational liquid level in the centrifugal chamber, which is exposed to the direct action of the electromagnetic field, has been estimated. It has been established that the effect of rotation of the total liquid volumehas been achieved at the height of application of electromagnetic field, which is 0.2—0.3 of the total fill height. Increasing the height of the application of a magnetic field leads to the capture of the upper layers of the liquid.Conclusions. There have been proposed a new design of magnetodynamic tundish (MD-T) for continuous casting of steel. The use of tundish with a rotational motion of the flow may significantly reduce the number of large oxide inclusions (larger than 10 µm) in steel. The device has been successfully tested and its application will improve the quality of cast billets, extend the functionality of equipment and technologies, and enable the realization of modern high-efficiency processes of continuous casting.

Investigation on flow field and heat transfer characteristics of film cooling with different swirling directions for coolant flow

In this paper, a hexagonal prism inlet chamber is used to form a swirling flow for the film cooling, and three kinds of compound angle of film hole ( γ = 10°, 20°, 30°) with clockwise swirling or counterclockwise swirling are used for numerical simulation studies. The influence of different compound angles of film hole and the swirling directions for the film cooling effectiveness are obtained. The results show that the film cooling effectiveness and spanwise cooling coverage range of the clockwise swirling or counterclockwise swirling flow both are low when the compound angle of film hole is 10°. With the increasing compound angle of film hole, the kidney shaped vortex of film hole exit gradually weakens until it disappears, which reduces the entrainment effect by the coolant jet. So that the spanwise coverage range of two swirling modes is obviously improved. When the compound angle of film hole is 30° compared to 10°, the average spanwise film cooling effectiveness of clockwise swirling and counterclockwise swirling are increased by about 133.75 and 212.6%, respectively. The average spanwise film cooling effectiveness on the downstream of film hole for counterclockwise swirling is increased by about 140% compared with clockwise swirling.

Flow Control of Radial Inlet Chamber and Downstream Effects on a Centrifugal Compressor Stage

Radial inlet chambers are widely used in various multistage centrifugal compressors, although they induce extra flow loss and inlet distortions. In this paper, the detailed flow characteristics inside the radial inlet chamber of an industrial centrifugal compressor have been numerically investigated for flow control and performance improvement. First, the numerical results are validated against the experimental data, and flow conditions inside the inlet chambers with different structures are compared. They indicate that, in the non-guide vane scheme, sudden expansions, tangential flows and flow separations in the spiral and annular convergent channels are the major causes of flow loss and distortions, while using guide vanes could introduce additional flow impacts, separations and wakes. Based on the flow analysis, structure improvements have been carried out on the radial inlet chamber, and an average increase of 4.97% has been achieved in the inlet chamber efficiencies over different operating conditions. However, the results further reveal that the increases in the performance and overall flow uniformity just in the radial inlet chamber do not necessarily mean a performance improvement in the downstream components, and the distribution of the positive tangential velocity at the impeller inlet might be a more essential factor for the efficiency of the whole compressor.

Effects of Inlet Chamber Structure of the Control Stage on the Unsteady Aerodynamic Force

Blade fatigue fracture is the main factor affecting the safe operation of the turbine and the aerodynamic exciting force caused by partial admission accelerates the fatigue failure of the control stage blade. In this paper, based on the three-dimensional unsteady flow research of 300MW control stage, a new type of inlet chamber structure is proposed, which can reduce the local aerodynamic exciting force effectively. The performance of original structure and new structure is compared at 0.7 partial admission operation condition in details. Firstly, the paper gives the overall performance of the control stage under the two structures. It is proved that the new inlet chamber structure proposed in this paper only has a slight influence on the overall performance, which is shown as mass flow, power and efficiency. Secondly, distributions of flow parameters such as pressure, static entropy and axial velocity at the stator inlet and rotor inlet are given in the paper. The new structure is found to alleviate the sudden change of flow parameters such as pressure at the inlet steam chamber transition region. Finally, five key points of axial aerodynamic force and seven key points of tangential aerodynamic force are captured to illustrate the influence of partial admission on instantaneous aerodynamic exciting force. Further, the mechanism of new inlet chamber structure on local aerodynamic exciting forces is explained. The result shows that the new inlet chamber structure can reduce the local axial aerodynamic exciting force up to 13% and reduce the local tangential aerodynamic exciting force up to 29.7%, which is beneficial to improve the safety and reliability of the turbine operation.