Glass Heat Exchangers
SIGMA heat exchangers provide the optimum solution for all requirements encountered because of the wide range of heat exchangers available. Heat exchangers are used for condensation of vapours or cooling of gas or cooling of liquids. Two basic types of glass heat exchangers are available, Coil type and Shell and tube type. Glass coil type heat exchangers are available as condensers, boilers and immersion heat 2 exchangers with heat transfer areas up to 8m. Shell & tube type heat exchangers are designed for use with tubes in the widest possible range of corrosion resistant materials. Shell & tube type heat exchangers are available with glass or Mild Steel (MS) Shells in combination with glass tubes as standard. The advantage of using Shell & Tube type heat exchanger are larger heat transfer area in single unit, Low-pressure drop, Easy tube replacement.
Glass Coil Heat Exchangers
Coil type heat exchangers are all glass design where coil battery is welded directly to glass jacket. This is of importance for plants which have to confirm to GMP requirements since it ensures that product & coolants cannot come in contact with each other. Coil type heat exchangers are mainly used as condensers or coolers. They can also be used for heat transfer between liquids & gases. Turbulent flow is ensured even in large bore heat exchangers since coil layers are offset & fill the flow cross section to great extent.
Following points should be taken in account while using coil type heat exchangers.
1. When connecting coolant lines to coil type condensers; flexible hose or bellow should be used to avoid transfer of stresses to the glass
2. Use of steam in coil should be avoided.
3. Coolant should not be allowed to be heated up to boiling point.
4. Coolant control valve should be turned on slowly particularly when air is present in the coils.
5. Complete drain of coolant should be allowed.
6. Brine can be used in coil in close circuit with suitable precaution against water hammering.
7. Vapour should be passed through shell only.
8. Maximum pressure of coolant should be 2.7 bar
9. Freezing of water in the coil should be avoided.
10. Condensers should preferably be mounted in vertical position.
11. Heat exchangers should be mounted in series to provide large surface area.
Typical Heat Exchanger Arrangement
The heat transfer coefficients also varies from one size of condenser to another but as a guide, the table below given as indication of the performance of condenser at atmospheric pressure, using water (inlet temperature 30 C) as coolant in the coils and steam condensing in the jackets.
The figures do not show the maximum performance of the units but are a general indication of typical working conditions.
The table below shows figures calculated on this basis for the condensation of steam at atmospheric pressure and a cooling water throughput for a maximum pressure drop of 2.5 bar in the coils (inlet temperature 30°C).
COIL TYPE BOILERS
Coil type boilers are predominantly used as circulatory evaporators. They are used for vaporizing liquids by passing steam in the coils. Boilers are made by fusing no of parallel coils in the glass shell. Boilers coils are designed to provided bigger cross section in shell side as compared to condensers. The maximum permissible steam pressure at inlet in coil is 3 bars for boilers. This o pressure can provide temperature of 143 C with saturated steam. Higher temperature can be achieved by using suitable thermic fluid.
Following points should be taken in account while using coil type boilers.
1. Flexible hoses should be used on coil inlet & outlet.
2. Steam inlet line should be adequately trapped to avoid possibility of steam hammering.
3. Start up by pass valve should be installed on coil outlet to clear the line of very heavy condensate flow produced on start up.
4. Control valve & pressure gauge should be placed very near the steam inlet of the coil.
5. Coil type boilers should not be fitted at bottom of columns or vessels as adequate circulation cannot be guaranteed in these locations.
6. Boiler should be mounted in an external circulatory loop as shown in figure.
7. Boilers can be mounted in series to provide larger heat transfer area.
8. Preheated liquids should be used for better result in boilers.
9. The steam pressure should always be adequate enough to ensure effective & smooth condensate removal. This pressure will vary on the size of boilers.
The maximum permissible steam pressure at the coil inlets of boilers is 3.0 bar.g. which is equivalent to a temperature of about 143°C with saturated steam. Higher temperatures can be achieved by using heat transfer fluids.
The heat transferred in most size can be considered on average as 400 W/m²K a steampressure in the coils of 3.0 bar.g, although this figure declines marginally at lover pressure.
The table shows typical performances of boilers indicating the amount of water evaporatedat atmospheric pressure with steam in the coils at various pressure.
Note : if the feed is cold, the performance of the boiler will be only about 85% of the figures quoted.
IMMERSION HEAT EXCHANGERS
Immersion heat exchangers are used to control exothermic reactions in the glass vessels They can be used in vessels with wider bottom outlet
Following points should be taken in account while using coil type boiler
1. Immersion heat exchangers are not recommended for use with products, which have a tendency to crystalise.
2. The coils must always be completely immersed in liquid.
Liquid coolers are used typically for the cooling of products from distillation columns and can be connected directly to the reflux head in a column. The product flows from top to the bottom of the unit through the coil battery across which the cooling water flows from bottom to top in the shell. Liquid coolers provide more resident time to the product to be cooled.
Vent condenser is installed before vacuum pumps or in vent gas lines to remove any components in vapour form still remaining in the gas stream after the main condenser. Their compact design makes them ideal for fitting directly in pipe work without the need for any reduction.
Glass Shell And Tube Heat Exchangers
Shell & tube exchangers are used particularly where large heat transfer area is required in combination with efficient heat transfer & compactness. These are widely used in industry for duties like cooling, heating, condensation, evaporation etc. They can be designed for single pass or multipass on tube side as per your requirement. The overall heat transfer coefficient in shell and tube heat exchanger is about three times higher then in coil type heat exchangers. Whenever requirement of heat transfer area is high; shell & tube heat exchanger is the only alternative. The pressure drop of coolant in shell & tube heat exchanger is minimal compared to approximately 2 kgs in coil type heat exchanger.
Range of the models
The glass tube are sealed individually into PTFE tube sheet with special PTFE sockets and packing. This unique ferrule type sealling arrangment permits easy replacements and cleaning of tubes. Baffles on shell side ensure improved heat transfer by increased turbulence. Further details of construction can be seen in the diagram.
1 METAL/ GLASS BONNET
2 PTFE TUBE SHEET
3 THREADED BUSH
4 GLASS TUBE
6 METAL/ GLASS SHELL
7 PTFE TUBE
8 TIE ROD IN PTFE
9 CASTIRON FLANGE
11 SCREWED ROD OR NUT
SHELL & TUBES
All Glass Tubes have an external diameter of 14mm and a wall thickness of 1.5mm (min.)
Orientation of branch connections can be changed on request.
All Glass Tubes have an external diameter of 14 mm and a wall thickness of 1.5mm (min.)
Orientation of branch connections can be changed on request.
Permissible Operating Conditions
For both coil type and shell and tube heat exchangers the permissible operating conditions for glass shell and headers are based on the diameter.
All Heat Exchangers can be operated under full vacuum.
Operating Temperature Range : (–) 40°C to 200°C on either side.
Diff. temperature : <120°C]
For shell and tube type heat exchangers, the permissible operating conditions for steel shell and bonnet can be determined from the table.
Performance & design data
Table given below indicates performance of glass shell and tube heat exchanger in several typical application. More specific advice can be given on receipt of details.
Generally two types of supports are used in shell and tube heat exchanger depends upon MOC of shell & tube heat exchangers.
MOC of these supports is MS.