Heat exchanger series is the most advanced design of polyblock Heat Exchangers. These are constructed from identically formed impervious graphite blocks with two types of passages viz short radial passages of 100 to 150mm length converging into a central cavity and short length axial passages with remixing of all the axial tube fluids in a mixing cum redistribution channel every 150 to 300 mm travel of the axial fluid. This particular feature of hydraulic design gives abundant turbulence even at low flow rates and enhances the ‘U’ and reduces the fouling & scaling drastically. The effect of high ‘U’ and lower fouling coefficient ‘s’ is that for the same heat duty the HTA value is lower. Due to their main features of robustness, high mechanical strength and exceptionally long working life, these heat exchangers are widely used in Pharmaceutical Industries, pesticide and fumigant sectors, Dye Stuffs, other Chemical Process Industries, petrochemicals, Phosphate Fertilisers and Pickling lines of Steel Rolling Mills etc.

• Heat exchange between two corrosive liquids.
• Condensation of corrosive organic & inorganic vapors.
• De-superheating of vapors, Partial Condensation & sub-cooling.

The heat exchanger assembly is made from a stack of cylindrical impervious graphite blocks, depending upon the HTA requirement and the desirable fluid flow rates.The stack of blocks is fitted with headers at both the ends.The graphite blocks and headers are housed in an MS shell for service fluid passage and also to impart protection and mechanical strength to the assembly. To separate the blocks and isolate the flows, teflon gaskets are used between each blocks. The stack of blocks is held tightly under compressive load using disc or spring washers on long pin bolts and nuts assembly. Deflector plates are used on entry nozzles to avoid direct impingement. Isolating Bellows are require on each of the inlet/outlet nozzles.

Process Fluid flows through the main axial passage of the graphite header and gets distributed into multiple axial passages and enters middle block. Then it passes through short axial passages and reaches the mixing cum redistribution channel before entering the next block. The same pattern is followed afterwards till the process fluid is collected by the lower header.

Service fluid flows through the radial passages of the 1st block to the central passage and then passes through the central passage to the second block. Then in the second block it passes from central passage to the radial passage and gets remixed with all the radial passages in the outer radial recess between the graphite block and the cylindrical holder. From this outer common channel it gets redistributed into the radial passages of the next block. The same pattern is followed afterwards till the Service fluid is collected by the exit nozzle of the bottom holder. The process fluid and service fluid are kept apart by teflon gaskets at the interface of each block with the next block.

Case I. Cold fluid at wet bulb temperature.

• Crack open the RT/cold fluid inlet nozzle valve keeping the corresponding outlet valve fully open.
• Let the inner contents get flushed out and then gradually close the RT/cold fluid outlet valve fully.
• Now open the inlet valve of the RT/cold fluid full.
• Establish the flow rate of the RT/cold fluid by gradually increasing the RT/cold fluid outlet valve opening.
• Now Crack open the hot fluid inlet nozzle valve keeping the corresponding outlet valve fully open.
• Ensure that the PRV in case of steam is set at < 4 kg/cm2 . In case of thermostat cutoff the temperature is set at <150°C.
• Let the inner contents get flushed out and then gradually close the hot liquid outlet valve fully or in case of steam, leave it fully open.
• Now full open the inlet valve of the hot fluid.
• Establish the flow rate of the hot fluid by gradually increasing the outlet valve opening. or in case of steam regulate the inlet valve appropriately.

Case II. Cold fluid at below wet bulb temperature.

• Establish the hot fluid stream first as per the procedure given above for hot fluid (not Steam). If hot fluid is steam, then use the procedure for startup with steam as given above.
• Establish the below wet bulb temperature cold fluid stream flow as per the procedure given above for hot fluid.