Re-Using Vent gas of calciner as heat source for

Fluidised bed dryer of Plant-04

MENTOR :Yati varshneya

SUBMITTED BY:Priyanka Agrawal

Contents

1. Introduction2. Heat flowing out of calciner vent.3. Heat required in FBD4. Modification required5. Suggestions

Introduction

Plant-04 is an absorbent making plant which manufactures chlorine and sulphur guard.

These absorbents are used in the petroleum refineries for absorbing the impurities like sulphur and chlorine from crude oil.

The basic unit operation involved in manufacturing of these absorbent are mixing, Granulation, Drying, Calcination, Screening.

MixingPan

Granulation

Fluidised Bed Drying Calcination Screening

Flow sheet of Material Flow Introduction

Introduction

In plant-04, 5 different types of absorbent are produced which differ in their composition and method of manufacturing.

In manufacturing of two of these products both drying and calcination are required.

So, for this the hot gas coming out of calciner vent can be used as heat source for the fluidised bed dryer.

The production of this product is approximately 200 MT/month and is produced for four months/based on S&OP in a year.

Heat flowing out of calciner vent

39% recycle

Vent gas

~2500m3/hrT = 260°C6 lakh KJ

T = 700°C

Hot gas out

4500m3/hr

Schematic Diagram of Calcination Process

Heat flowing out of calciner vent

Approximately 6 lakh kilo joule of heat is coming out from calciner vent.

Blower air quantity (m3/hr) 4500Recycle value 0.39Vent gas (m3/hr) 2745Approx. Vent flow rate (m3/hr) 2500Temperature of vent gas °C 260Reference temperature °C 61Heat coming out (KJ/hr) 6,12,484.7

Presently calciner is operated at 39% recycle of vent gas back to calcinerand rest is released into the atmosphere.

The vent gas is at a very high temperature of 260°C so this heat can be utilised. In calculation the value of the flow rate of vent gas is approximated to 2500m3/hr.

Heat coming out = flow rate*density*specific heat*(Temp. Of vent gas-Reference temp)

Heat required by FBD

The main objective of FBD is to remove moisture of material and for which hot air is passed through FBD.

So the heat load on FBD can be calculated in two ways:

1. Heat required by material.2. Heat supplied to air by burner

552 kg/hrT = 25°C

T = 60 °C

Heat required by FBD

1. Calculating Heat required by Material

Control Volume

Mixing Chamber

Assumption Heat capacity of material in and out are same. In the FBD only moisture gets removed, no CO2 removal. The amount of material being carried to the cyclone separator by

air is negligible.NOTE: The analysis is based on the data taken from 7-june-2015 to

14-june-2015.Formulae usedHeat load on FBD = heat needed to vaporise water + heat needed to raise material

temp.Heat needed to vaporise water = water to be vaporised *latent heat of vaporisation of

water

Heat needed to raise material temp. = mass flow rate of material*specific heat of material*(outlet temp. - inlet

temp.)

Heat required by FBD

Material flow rate(kg/hr) 552. 00 Temperature at inlet(°C) 25.00 Temperature at outlet(°C) 60.00 Moisture content at inlet (%) 18.00 Moisture content at outlet(%) 2.00 water to be vaporised(kg/hr) 88.32 Latent heat of vaporisation(KJ/kg) 2,258.00 Heat needed to vaporise water(KJ/hr) 1,99,426.56 Cp of material(KJ/kgK) 0.85 Mass of dry Solid (kg/hr) 452.64 Heat needed by material(kg/hr) 13,488.22 Heat load on FBD (kg/hr) 2,12,914.78

Approximately 2.2 lakh kilo Joule of heat needed to be supplied to the materiall

Heat required by FBD

2. Calculating Heat supplied to air by burner

7300m3/hrT = 61°C

T = 35°CT = 35°C

Heat required by FBD

Mixing Chamber

To calculate the flow rate of air Anemometer was used.At different positions velocity were taken under following situation 1. The damper at fresh air inlet of fbd was fully opened.2. The velocity measurements were done after removing the mesh.

Assumption:3. Considered the pipe to be perfectly cylindrical at the cross section

where velocity was calculated at different points.2. Flow is Turbulent means flatter velocity profile.3. The average velocity across the cross section was taken in calculation.4. The burner is 98% efficient.

Formulae Used:Flow rate = flow area* average velocity

Heat supplied to air by burner =air flow rate*density*specific heat of air*(temp. at fbd inlet – fresh air temp.)

Heat required by FBD

Flow rate of air (m3/hr) 7,314.06Temp of air at inlet(°C) 35.00Temp of air at fbd in (°C) 61.00heat supplied to air by burner (KJ/hr) 2,34,117.42

Approximately 2.34 lakh kilo Joule of heat needed to be supplied to be supplied by the burner.So, from the two methods of calculation heat required by FBD can be approximated to 2.34 lakh KJ.

Heat required by FBD

LPG requirement for fulfilling this heat requirement

heat supplied to air by burner (KJ/hr) 2,34,117.42Calorific value (KJ/kg) 48,070.00burner efficiency 0.98LPG required(kg/hr) 4.97The LPG required by theoretical calculation comes out to be 5kg/hr

Plant LPG totalizer reading for duration under consideration is 2.05kg/hr but is 4 kg/hr also in other days.

The possible reason for this congruity can be improper calibration of LPG totalizer.

Modification required

Pipe of Length =6m including the two 90°bend.

Diameter of pipe = 300mm excluding insulation, same as diameter of vent line.

The line would be installed diagonally from the point near the place wherethe 39% recycle valve is to the point on the roof above which dilution chamber is.

Butterfly valve is required to control flow of gas depending on the temperature required at FBD inlet.

Fabric filter will be required to remove 70 mg/m3 of particulate matter present in vent gas.

Line to be added to present system

Modification Required

Mixing Chamber

39% recycle

4500m3/hr

33 – 71% recycle

Length = 6m Dia = 300mm

Pressure Drop = PD by fabric filter + 30Pa

2500 m3/hrVelocity = 10m/sT=260°C

Modification Required

Flow rate of vent air= 850- 1800m3/hr

Flow rate of fresh air= 5550- 6500m3/hr

Flow rate at FBD in= 7300m3/hr

Mixing Chamber

MixingChamber

Hot AirGenerator Bu

rn er

Supply Fan

Hot air Generato

rBurn er

BlowerGround floor

1st floor

2nd floor

Vent Gas

39% RecycleL=350mL=275m

Temp. of air at FBD inlet(°C) 61 90Temp of vent air(°C) 260 260Temp. of fresh air(°C) 35 35Flow rate of vent air (m3/hr) 2500 2500Flow rate of FBD inlet (°C) 7300 7300Fraction of vent air 0.33 0.71Flow rate of vent air(m3/hr) 843.56 1784.4Flow rate of fresh air (m3/hr) 6,456.4 5515.56Heat required by FBD(KJ/hr) 2,33,667.5 494296.6Calorific value KJ/kg 48,070.00 48,070.00burner efficiency 0.98 0.98LPG consumption (kg/hr) 4.960188267 10.49270595LPG consumption per month(kg/month) 3571.335552 7554.748284cost of LPG(Rs./kg) 40 40Cost saved (Rs.) per month 1,42,853.42 3,02,189.93

Modification Required

Suggestions

Screening should be done just after granulation process and oversized particle should be recycled.

Can control the burner firing from FBD inlet temp. reading instead of cyclone inlet temp.

One RTD should be placed near the outlet of the FBD for getting correct value of product temp.

Thank You