Shell-and-tube heat exchanger - preheater

Contents

Introduction

General information about heat exchangers

Surface heat exchangers

Mixing heat exchangers

Shell and tube heat exchanger

Diagram Description

Process calculation

Constructive calculation

Mechanical calculation

Safety precautions

List of literature

Introduction

Heat exchangers, or heat exchangers, are devices for transferring heat from some media (hot heat carriers) to others (cold heat carriers). Heat exchangers are used for heating and cooling substances in various aggregate states, evaporation of liquids and condensation of vapors, distillation and sublimation, absorption and adsorption, melting of solids and crystallization, removal and supply of heat during exo and endothermic reactions, etc. Accordingly, heat exchangers are referred to as preheaters, coolers, evaporators, condensers, distillers, sublimators, melters, etc.

Heat exchangers according to the heat transfer method are divided into surface ones, where there is no direct contact of heat carriers, and heat transfer occurs through a solid wall, and mixing ones where heat carriers contact directly. Surface heat exchangers, in turn, are divided into recuperative and regenerative, depending on the simultaneous or alternating contact of the heat carriers with the wall separating them. Surface type heat exchangers are also classified by purpose (heaters, refrigerators, etc.); in the mutual direction of heat carriers (direct flow, countercurrent, mixed current, etc.); by heat exchange surface material; by number of moves, etc.

Surface heat exchangers

Recuperative heat exchangers

Recuperative heat exchanger is a heat exchanger in which hot and cold heat carriers move in different channels, in the wall between which heat exchange takes place. Under unchanged conditions, the parameters of the coolant at the inlet and in any of the channel sections remain unchanged, independent of time, that is, the heat transfer process is stationary. Therefore, recuperative heat exchangers are also referred to as stationary heat exchangers. Recuperators can operate in both periodic and continuous modes

Depending on the direction of movement of heat carriers, recuperative heat exchangers can be direct-flow in parallel movement in one direction, counter-current in parallel opposite movement, as well as cross-current in mutually perpendicular movement of two interacting media.

The most common recuperative heat exchangers in industry:

- shell and tube heat exchangers,

- element (section) heat exchangers,

- double-tube heat exchangers of pipe-in-pipe type,

- twisted heat exchangers,

- submersible heat exchangers,

- irrigation heat exchangers,

- ribbed heat exchangers,

- spiral heat exchangers,

- plate heat exchangers,

- plate-finned heat exchangers,

- graphite heat exchangers.

2) Regenerative heat exchangers

In regenerative surface heat exchangers, heat carriers (hot and cold) contact the solid wall in turn. Heat accumulates in the wall when in contact with hot heat carrier and is released when in contact with cold heat carrier. Regenerators are periodic sets.

Mixing heat exchangers

Mixing heat exchanger (contact heat exchanger) - a heat exchanger designed to carry out heat and mass transfer processes by direct mixing of media. The most common PSA steam-water jet devices are jet-type heat exchangers, which use a jet injector at their core. Mixing heat exchangers are structurally arranged simpler than surface ones, more fully using heat. However, they are suitable only in cases where, according to technological conditions of production, mixing of working media is permissible.

Contact heat exchangers find great use in heat recovery plants for flue gases, exhaust steam, etc.

Functional Diagram Description

The initial mixture is supplied to the storage tank E1, which is necessary for uniform power supply of the rectification column of RK. By pump H1, the mixture is supplied to the feed tray in RK, passing through heat exchanger - preheater P. In the preheater of the initial mixture, the mixture is heated to boiling temperature, due to the supply of heating steam to the tube space. The initial mixture entering the boiler at boiling temperature flows down the trays to the lower part of the column. At each stage (tray), liquid flowing down and vapors rising up the column interact, while a high-boiling component (HC) condenses from the vapors, and a low-boiling component (HC) evaporates from the liquid. As a result of this interaction, almost pure NC leaves the top of the column at each stage, and VK is removed from the bottom of the column. The vapors in the cube are obtained by evaporating the bottom liquid in the heat exchanger - reboiler K. The vapors withdrawn from the upper part of the column are sent to the heat exchanger - condenser D. Due to the supply of cooling water to the pipe space, the vapors are condensed and withdrawn from the apparatus at the condensation temperature. Further, the condensate stream is divided into two parts: reflux and distillate. Reflux refers to part of the condensate returning to the top of the column for irrigation. Distillate is a finished product (target), which is first cooled in a heat exchanger - refrigerator X2, and then supplied to a storage tank E3. Distillate is pumped by H4 pump to consumer. The bottom residue (VC) is removed from the cube and sent to the heat exchanger-cooler X1, after which it is accumulated in the tank E2, from where it is pumped by the pump H3 to the consumer.

The rectification plant is a complex controlled facility, so it includes a large number of instruments and automation, a warning and alarm system, as well as interlocks.