Shell and Tube type Heat Exchanger

Introduction:

We have played an important part in the design, manufacture and installation for an important client located in Raipur, Madhya Pradesh. The requirement was for a  9.0 MVA Ferro Alloy Furnace for the reduction of the Exhaust Gases.

Our client had been facing the problem in the furnace because the Gas Cleaning Plant (GCP)had temperature reduction done by FD cooler, but the working efficiency was very poor and we at Clair proposed to assess the performance of the GCP.

On visiting the site, the basic type of application and product line was understood that is given in Table 1 while, the technical specifications are mentioned in Table 2.

There were many factors on which we proposed the following:-

• Forced Draft Coolers are installed to cool the hot process gases to desired temperatures and filter the dusty gases in APC equipment
• Forced Draft Coolers use Cooling air Fans to cool the hot process gases
• Forced Draft Coolers, in general are shell & tube type, with hot dusty gases inside tubes & cooling air over the tubes
• Cooling air fans can be either Axial or Centrifugal type depending on site space availability
• Number of passes – Based on process parameters and target temperature gradients

Data/ Table:

Table 1: Basic Details collected during Visit

Table 2: Technical Specifications Of Heat Exchanger

Observations:

Clair took up the challenge and following solution was proposed and implemented:

• The provided FD Cooler is Air to Air FD Cooler with 3 No. passes installed in series arrangement
• Since the Air to Air heat transfer is very low compared to any other heat exchange, the care has been taken to select appropriate overall heat transfer coefficient
• Since the flue gases contain the dust, the probable dust coating on tubes is also considered in deciding the heat transfer area required
• The tube diameter selected is 135.7 mm ID considering the dust concentration of flue gases and the large diameters avoids the problem of choking of the tubes
• The gas velocities inside the tubes has been considered taking into account the abrasive nature of the dust
• Three pass FD Cooler is designed for efficient cooling of the gases
• Gas flow in tubes in every pass with appropriate velocities to avoid dust deposition in the tubes
• Top entry for the first pass is designed for uniform gas distribution in the tubes
• Tubes are arranged in triangular pitch for better contact between cool air and tubes
• Axial fans are selected as cool air fans for better heat transfer
• Hoppers are provided for each pass. The dust from the hoppers is continuously transported via dust disposal system with Knife edge gate valve, dome valves & conveying system of Mecgale make

Clair successfully implemented and commissioned the installation of NewShell and Tube type Heat Exchanger in 2018with  emissions of 80,000 Nm³/Hr at 280^oC.

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