The Choice of the Optimal Retrofit Method for Sections of the Catalytic Reforming Unit

Hydrotreating section and catalytic reforming section of catalytic reforming unit L-35-11/600 were examined in this paper. This unit was designed for processing large fraction of naphtha by catalytic reforming in order to obtain components of gasoline with an octane number 78-85 points. Pinch diagnostics for these sections was carried out. Comparative economic analysis of their effectiveness after the proposed retrofit was performed for each section separately and for the total their flowsheet. The implementation of the Pinch Method for hydrotreating section will reduce energy intensity by 2.2 MW. Energy consumption for catalytic reforming section reduced by 6.4 MW. Energy consumption for joint integration of hydrotreating section and catalytic reforming section reduced by 11.4 MW. Therefore, it was concluded that Pinch design for these sections of catalytic reforming unit L-35-11/600 is most advisable to carry out for the two sections together

A Multi-Level Mathematical Model of the CO Catalytic Conversion Process

This paper presents a three-level modelling approach to the catalytic carbon monoxide oxidation in a temperature range between 400 K – 800 K. The first level involves the description of the chemical kinetics for the exothermic reactions on the catalyst surface. The second level models the thermal and hydrodynamic processes in the boundary diffusion layer between the catalyst surface and the reactive stream. Finally, the third modelling level focuses on the representation of the hydrodynamic and thermal properties for the bulk multi-component gas flow at various gas velocity and temperature ranges. The dynamic behaviour of the reactive system has been studied through simulated runs

Intensification of Heat Transfer Processes

New challenges in efficient heat recuperation arise when integrating renewables, polygeneration and combined heat and power (CHP) units with traditional sources of heat in industry and the communal sector, as it is shown by Klemeš et al. (2010). Heat transfer enhancement is an efficient technique to increase energy saving when retrofitting heat exchangers or designing a new heat transfer system. By implementing intensified techniques in existing exchangers, higher heat transfer coefficients can be achieved, leading to higher heat exchange duties allowing a reduced size of heat transfer equipment and the associated benefits (especially improving heat transfer performance). Intensification techniques provide: (i) Reduction in size of a heat exchanger for a given duty; (ii) Increase in capacity of an existing heat exchanger; (iii) Reduction in approach temperature difference; or (iv) Reduction in pumping power. Conventional enhancement techniques include tube-side enhancements (i.e. enhanced surface tubes, internal tube fins, coatings, fluid additives, mechanical mixing devices, twisted-tape inserts, coiled-wire inserts, etc.); shell-side enhancements (i.e. externally enhanced surface tubes, external tube fins, coatings, fluid additives, helical baffles, etc.). The compact heat exchangers such as tube-fin, plate-fin and plate heat exchangers are using heat transfer intensification and offer significant reduction in size, weight and cost of heat recuperation equipment. Developments in mini- and micro- channel heat exchangers are offering new possibilities of heat transfer intensification in channels of very small hydraulic diameters. Recently such intensification has been widely studied in the process industry from the point of view of individual heat exchangers. Combining several enhancement techniques can achieve higher energy savings when compare to implementing a single technique. It is difficult to identify which intensification technique is more suitable in a certain design, or which combinations of enhancement techniques are expected to contribute the most in compound augmentation applications. This work will survey current practices and review recent advances in enhancement techniques from an economic and performance standpoint

Optimal design of plate-and-frame heat exchangers for efficient heat recovery in process industries

The developments in design theory of plate heat exchangers, as a tool to increase heat recovery and efficiency of energy usage, are discussed. The optimal design of a multi-pass plate-and-frame heat exchanger with mixed grouping of plates is considered. The optimizing variables include the number of passes for both streams, the numbers of plates with different corrugation geometries in each pass, and the plate type and size. To estimate the value of the objective function in a space of optimizing variables the mathematical model of a plate heat exchanger is developed. To account for the multi-pass arrangement, the heat exchanger is presented as a number of plate packs with co- and counter-current directions of streams, for which the system of algebraic equations in matrix form is readily obtainable. To account for the thermal and hydraulic performance of channels between plates with different geometrical forms of corrugations, the exponents and coefficients in formulas to calculate the heat transfer coefficients and friction factors are used as model parameters. These parameters are reported for a number of industrially manufactured plates. The described approach is implemented in software for plate heat exchangers calculation

The Precise Definition of the Payload Tube Furnaces for Units of Primary Oil Refining

The article considers the primary oil refining unit AVDU A12/2 in the mode without vacuum unit. In this paper carried out extraction of data on process flows and equipment, tabulated streaming data. It is performed modelling of primary oil refining unit in the software package Unisim Design to refine the data. It was determined the potential energy savings through the using methods of the pinch analysis, done the project of reconstruction of AVDU A12/2 with the modelling in program Unisim Design to confirm the performance of the project. The amount of heat loss in the heat exchange equipment and pipes was calculated, have developed a method for the accurate determination of the payload tube furnaces

Targeting Minimum Heat Transfer Area for Heat Recovery on Total Sites

This paper upgrades the Total Site integration methodology, when accounting for a trade-off between capital and heat recovery by selection of optimal temperature levels for intermediate utilities and therefore, decrease capital cost. Heat transfer area for recuperation in Total Site is a two-fold problem and it depends on the Sink Profile on one side and on the Source Profile on another. The resulting temperature of intermediate utility is a result of a trade-off since the heat transfer area on Source side is decreasing, when temperature of IM is decreasing, however increased on Sink side. In the opposite higher intermediate utility temperature leads to higher area on the Source side and lower on Sink side. The temperature of each intermediate utility may be varied between specified lower and upper bounds subject to serving the Sink and Source Profiles

Computer Aided Design of Plate Heat Exchangers

The computer aided design of plate heat exchanger with mixed grouping of plates is considered. It is formulated as the mathematical problem of finding the minimal value for implicit nonlinear discrete/continues objective function with inequality constraints. The optimizing variables include the number of passes for both streams, the numbers of plates with different corrugation geometries in each pass, the plate type and its size. To estimate the value of objective function in a space of optimizing variables the mathematical model of plate heat exchanger is developed. To account for thermal and hydraulic performance of channels between plates with different geometrical forms of corrugations, the exponents and coefficients in formulas for heat transfer coefficients and friction factors calculation are used as model parameters. The procedure and software for numerical experiment to identify model parameters by comparing the calculation results with those obtained with free available in web computer programs of plate manufacturers is developed. The sets of such parameters are obtained for a number of industrially manufactured plates. The described approach is implemented as software for plate heat exchangers calculation

CFD Modelling of Hydrodynamics and Heat Transfer in Channels of a PHE

Plate Heat Exchangers (PHEs) are one of the most efficient types of contemporary heat exchangers with intensified heat transfer. They are commonly used in process industries due to their compactness, lower weight and cost, smaller space for installation and servicing compared to conventional shell-and-tube heat exchangers. Heat transfer in PHEs takes place in channels of complex geometry formed by corrugated plates placed abutting. The flow in such channels can be very complicated due to breakup and reattachment of the boundary layer, secondary flows and the small hydraulic diameter of the flow passages. The aim of this work is to compare a well-established and validated CFD code both with results obtained from an experimental PHE model using a corrugated plate commonly used in industrial applications and with existing correlations. The results show that CFD simulation can predict heat transfer rate and fluid flow behaviour in a range of Re numbers (8,900 to 27,650), with discrepancies up to 1 % and 6 % in terms of outlet temperature and pressure drop respectively. Modelling of the flow inside a single corrugation also allows for computation of the wall shear stress distribution which can be very useful in PHE applications where fouling is of particular importance

Total Site Integration for Coke Oven Plant

The process of benzene distillation and process of coal tar distillation being typical for East European countries is analyzed in this paper. The pinch analysis method was selected to perform a reconstruction project. According to principles of pinch analysis, new network diagrams are designed and capacity of heatexchange equipment is calculated. The using of "Total Site Profiles" showed the feasibility of heat pump integration. Heat pump integration allowed to reduce the external hot utilities usage on 368 kW and cold utilities usage on 368 kW. This project let to decrease the external hot utilities usage on 23 % and cold utilities usage on 24,13 %, and also offered the way of step-by-step retrofit of the plant

The Modified Analogy of Heat and Momentum Transfers for Turbulent Flows in Channels of Plate Heat Exchangers

The modification of Von Karman analogy for turbulent flow in channels of Plate Heat Exchangers (PHEs) is proposed. The resulting equation enables to calculate film heat transfer coefficients in PHE channel on a data of hydraulic resistance of the channel main heat transfer field, accounting for the influence of channel geometry, flow velocity and fluid properties. The comparison with experimental data for water flow in models of PHE channels main corrugated fields is presented. It is shown the good accuracy of prediction for film heat transfer coefficients. In the limiting case, where corrugations are parallel to plate axis, the results of calculations by proposed Equation are in excellent agreement with Equation published for straight tubes and channels by Gnielinski in 1975. The analysis of the Prandtl number influence on heat transfer is performed. It explains the difference of Pr powers, which varies from 0.6 to 0.3 at correlations reported in different experimental papers on heat transfer. The proposed Equation can be used for modelling of PHEs heat transfer performance in a wide range of different applications in process industries