Litr.survey

7/29/2019 Litr.survey

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Introduction:-As in previous years, a considerable effort has been devoted to research in traditional

applications such as chemical processing, general manufacturing, and energy conversion

devices, including general power systems, heat exchangers, and high performance gas

turbines. In addition, a significant number of papers address topics that are at the frontiers of

both fundamental research and important emerging technologies, including Heat and mass

transfer in paper drying process.

The present review considers the overall work done with paper industry literature

published in previous years.The papers are grouped into separate subject related sections and

then into subfields within these sections. Papers pertaining to heat transfer which were

published in previous years are as follow:1) Numerical and experimental investigation of paper drying: Heat and mass transfer with

phase change in porous media.

T. Lu, S.Q. Shen., online 12 January 2007.

2) A study of the spontaneous air flow through a moving porous medium.Jianyao Moua, G. Randall Straleyb, Xiaodong Wanga, 6 March 2003.

3) Heat and mass transfer in multicylinder drying, Part I. Analysis of machine data.Lars Nilsson., 6 May 2004.

4) Heat and mass transfer in multicylinder drying Part II. Analysis of internal and externaltransport resistances.

Lars Nilsson, 10 May 2004.

5) Cross-directional control of sheet and film processes.Jeremy G. Van Antwerp, Andrew P. Featherstone, Richard D. Braatz, Babatunde A.

Ogunnaike., 19 July 2006.

6) Improved web break strategy using a new approach for steam pressure control in papermachines.

Jenny Ekvalla, Tore Hagglund, 7 March 2008.

7) Energy assessment of Paper MachinesNaveen Bhutani, Carl-Fredrik Lindberg, Kevin Starr, Robert Horton., 14 June 2012.

8) Thermodynamic simulation of dryer section heat recovery in paper machines.

L. Sivill, P. Ahtila, M. Taimisto, 10 September 2004.

9) Design of robust heat recovery systems in paper machines.

Frank Pettersson, Jarmo Soderman, 9 June 2007.


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Title: - Numerical and experimental investigation of paper drying: Heat and mass transfer

with phase change in porous media.

Author: - T. Lu, S.Q. Shen.

Available: - online 12 January 2007.

In this paper they have modeled drying process with liquid and vapor mass

conservation equation, the liquidgas mixture mass conservation equation, and the energy

conservation equation. Also Numerical simulation and experimental investigation of whole

paper drying are done on actual paper machine. The drying parameters in boundary

conditions including the temperature of outer surface of the cylinder, the temperature and the

relative humidity of the air pocket were measured. The numerical results of paper sheet

temperature of the first 26th cylinders and the final moisture content after 78 cylinders agree

well with experimental data, which means the drying model is valid to predict the

performance of paper drying. They measured surface temperature of cylinder and the paper

sheet by infrared measurement. Also, the relative humidity and temperature of air in gas

pocket by digital hygrothermograph. Hence, this paper presents a model for paper drying

based on the fundamental equation for heat and mass transfer in porous media.The drying

model applied to a running paper machine is solved by numerical method based on practical

parameter which is measured by experiment.

They have given system description of paper drying as follows:

The most common drying system used in the paper industry is a multi-cylinder dryer

section, which consists of a series (20120 units) of cylindrical 0.752.0 m diameter cast-iron

dryer drums. The two-tier paper dryer section in Fig. 1 shows the four phases of the drying

process. The drying process for each cylinder can be broken down into the following phases:

Phase I: The sheet is in contact with the outer surface of the cylinder but is not covered with

the felt.

Phase II: The sheet remains in contact with the cylinder and is covered on its outer surface

by the felt.

Phase III: The sheet remains in contact with the cylinder but is no longer covered with the

felt (similar to phase I).

Phase IV: The sheet is no longer in contact with the dryer cylinder and is in an open draw,

where moisture can evaporate from both sheet surfaces.


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Fig.1:Schematic of Paper drying system in a paper dryer section.

The paper is threaded around each dryer, which is heated by condensing steam with

conduction as the major mode of heat transfer to the sheet. The drying felt is a highly porous

material whose main purpose is to hold the paper sheet in close contact with the dryer

cylinder to increase the heat transfer between the dryer drum and paper sheet, to help prevent

shrinkage and deformation of the paper sheet, to enhance the stability of the paper running.

Measurement point:-

A, C, E-Inlet Point; B, D- Outlet Point, F, G-Top and bottom points of cylinder,

H- Center point of gas pocket.

Phase definition:-II-contacting drying period; IV-Free movement drying period.

In phases I and III, which are a small part of the whole drying period, one side of

the paper sheet is in contact with the cylinder surface while the other is exposed to the small

region between the paper sheet and the felt which can easily become saturated which limits

vapor diffusion. Therefore, in the model phases I and III are combined with phase II to form

the contact drying period, interval AB, with interval BC as the free movement drying period.

As the sheet moves from C to D, the drying boundary conditions be reversed from interval

AB. Interval DE is similar to BC. Points A and C are defined as the cylinder inlets and points

B and D are the cylinder outlets. The inlet is the beginning of the contact drying period and

also the end of the previous free movement drying period while outlet is the end of the

contact drying period and the start of the next free movement drying period. The heat and

mass transfer processes differ in the contact drying period from those in free movement

drying period, resulting in gradients of the drying parameters such as moisture content,

temperature, and pressure in the paper sheet.


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Title: - A study of the spontaneous air flow through a moving porous medium.

Author: - Jianyao Moua, G. Randall Straleyb, Xiaodong Wanga,

Available: - 6 March 2003.

This paper addresses the issues such as the velocity distribution along the moving felt

and how the flow rate through the porous material correlates with the felt permeability and

thickness.In this paper, the spontaneous flow through a moving porous medium is modeled

with both analytical and computational models. In particular, computational approaches are

compared with existing experimental results and validated with an analytical model. The

purpose of this paper is to quantify the spontaneous air flow through the permeable felt and to

find out the important factors which could significantly affect the quality of the products as

well as the energy consumption. The goal of increasing evaporation rate is usually

accomplished by various pneumatic devices, the so-called blow boxes, which are currently

used in the industry. In general, in order to enhance the circulation in the pocket and to

efficiently flush out the moisture, hot air is introduced from the blow box to the dryer pocket

via the moving permeable felt where most of the evaporation occurs. Their main interest in

his work was to find out when the relative movement between the porous material and the

surrounding air arises, why and how the air is drawn through the moving porous material, and

what are the significant influencing factors?. They established two mathematical models

(a) Represents a long and narrow channel with a constant pressure drop across the entire

length of the model (the flow is assumed to be laminar), whereas model

(b) Represents a long channel with a finite width and a constant inlet flow rate. (The flow is

considered as turbulent).

By varying different design parameters such as the felt moving velocity and the

permeability, they conclude that:

1)The increase of the felt velocity, for a given felt permeability, will increase proportionallywith the spontaneous flow rate through the felt.

2) For a fixed felt moving velocity, there exists a certain permeability threshold beyondwhich the spontaneous flow will not increase further, and such a critical point depends on

the felt woven structure, the felt moisture level, and the various operating conditions.

3)The spontaneous flow velocity profile decreases from the high pressure area to the lowpressure area. Moreover, it has a linear monotonic distribution for low permeability and a

rather uniform distribution for high permeability.

4)The selection of the felt thickness is also relevant. In fact, the thickness of the felt isinversely proportional to the spontaneous flow rate.


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Title:-Heat and mass transfer in multicylinder drying, Part I. Analysis of machine data.

Author: - Lars Nilsson.

Available: -6 May 2004.

They Presented a mathematical model describing the heat and mass transfer in thedryer section of a paper machine which has been applied to production data from four paper

machines producing paper with basis weights ranging from 0.056 to 0.390 kg d.s./m2. The

mathematical model does not include a description of the heat and mass transfer processes

occurring within the drying web, assuming instead that the temperature and moisture

content remain homogeneous in the thickness direction.The web is treated as a water film

passing through the dryer section. The aim of his study involves investigating; by

comparing simulated results to actual machine data, whether detailed models for internal

heat and mass transfer within the sheet are necessary prerequisites for successfully

calculating the final sheet moisture content/machine velocity.A total of 163 data sets were

used for validating the model.The results of his study indicate that assuming instantaneous

redistribution of heat and water within the sheet is a good enough assumption for paper

machines producing paper with basis weights below approximately 0.16 kg d.s./m2.

Data sets from paper machines:

The model was tested on data from four different paper machines, producing paper of

basis weights ranging from 0.056 to 0.390 kg d.s. /m2. A total of 163 data sets were

collected from the four machines. Each data set contains information regarding the steam

pressures in all steam groups, the basis weight and the moisture content of the sheet before

the reel, the machine speed at the press section and at reel as well as the steam flow rates to

the paper machines.

Table 1: Data from four different paper machines.

Machine A B C D

Number of data sets 60 32 28 43Number of cylinders 51 49 40 93

Range of dry basis weights (g d.s./m ) 56101 65118 102159 189390

Range of machine speeds (m/min) 480789 477700 265446 199525

Range of production rates (ton/h) 1625 1724 1113 3751

Moisture content after press section (%) 60 60 66 56

Web temperature after press section (C) 40 40 40 40

Fitted value forhcont (W/m C) 590 590 470 366

The results of this study indicate that assuming instantaneous redistribution of heat and

water within the sheet is a good enough assumption for paper machines producing paper with

basis weights below approximately 0.16 kg d.s. /m2.


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Title: - Heat and mass transfer in multicylinder drying Part II. Analysis of internal and

external transport resistances.

Author: -Lars Nilsson.

Available: - 10 May 2004.

In this paper study investigates two modelstwo limiting casesfor the internal heat

and mass transfer in a multicylinder dryer: the first model assumes that complete

redistribution of heat and moisture in the thickness direction occurs instantaneously. The

second model assumes that moisture transfer occurs only by vapor diffusion and that heat

transfer takes place by conduction and condensation.

For simplicity, a set of standard data was used for setting boundary conditions and

initial/final conditions regarding temperature and moisture content for the drying process.

1. The multi-cylinder dryer was assumed to consist of 40 cylinders, all of them heated.2. The wrap angle of the web was assumed to be 225, and3. The relation between the time for passing the draw and the time for contact with the

cylinder was assumed to be 0.40 (tdraw/tcontact = 0.40).

4. The steam temperature was assumed to be 130 C,5. The temperature and moisture content of the air in the hood was assumed to be 80 C

and 15 mol%, respectively.

6. With regard to the initial conditions, the moisture content of the sheet after the pressSection was assumed to be 1.50 kg H2O/kg d.s. and the temperature 40 C.

7. After the dryer section 0.10 kg H2O/kg d.s. was assumed to remain in the web.Transport coefficients:-

1) Convective mass transfer coefficient was taken as kconv = 0.04 m/s,2) Effective diffusivity of water vapor in paper De = 4106 m2/s, and3) Heat conductivity of paper as k = 0.09 W/mC.

Using a set of transport coefficients leading to realistic drying rates, the limiting

basis weight is established as approximately 0.05 kg d.s. /m2, which is lower than the value of

0.16 kg d.s./m2, established previously by analysis of a number of sets of machine data from

four different paper machines. Still, the mathematical model including internal heat and mass

transfer (model II) probably underestimates the mass transfer rate within the web since

capillary flow and surface diffusion are not taken into account.


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Title: -Cross-directional control of sheet and film processes.

Author: -Jeremy G. Van Antwerp, Andrew P. Featherstone, Richard D. Braatz, BabatundeA. Ogunnaike.

Available: -19 July 2006.

This paper reviews recent developments in sheet and film process control with

particular attention to the effectiveness of existing techniques at addressing the critical

aspects of sheet and film processes.Sheet and film processes include polymer film extrusion,

coating processes of many types, paper manufacturing, sheet metal rolling, and plate glass

manufacture. Identification, estimation, monitoring, and control of sheet and film processes

are of substantial industrial interest since effective control means reduced usage of raw

materials, increased production rates, improved product quality, elimination of product

rejects, and reduced energy consumption.

General features of sheet and film processes:-

High-quality sheet and film products have uniform properties both across the sheet,

called the CD, and along the length of the sheet, called the MD.

Fig.2:- Generic sheet or film process with scanning gauge

The MD problem is generally dominated by the time delay of the process and this

may have the effect of the achievable closed-loop performance.The second main control

objective is the maintenance of uniform properties across the width of the machinethis is

referred to as the cross-directional (CD) control problem. This survey is primarily focused

on the CD problem because this is generally considered to be much more difficult than the

MD problem.Among the many defects which can occur are variations in the film thickness,

surface defects, low tensile strength, low impact strength, hazy film, blocking, and

wrinkling. A major source of defects is tear or breakage of the web or sheet, and

subsequently, the ability to produce product that meets quality specifications following aweb break.


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Title: - Improved web break strategy using a new approach for steam pressure control in

paper machines.

Author: -Jenny Ekvalla, Tore Hagglund

Available: -7 March 2008.

This paper presents a new strategy for steam pressure control during web breaks in the

paper machine. The aim was to restart paper production with the same drying properties of

the cylinder as before the break.A detailed physical dynamic model of the drying cylinder

has been developed. The accuracy of the model has been verified through experiments made

at the M-real paper mill in Husum, Sweden. Verifications are made both during normal

operation and during web breaks.

The main purpose of a paper machine is to produce paper at a high rate while also keeping a

constant quality. Modern paper machines must produce paper at a high speed with large

demands on the quality of the paper. A key problem in this effort is to control the machine in

such a way that the production is restarted as quickly as possible after web breaks. One of the

most common ways to dry paper is multicylinder drying. The moist paper web enters the

dryer section, which consists of 50100 steam heated cast iron cylinders. The moisture

content in the paper is controlled by adjusting the steam pressure in the cylinders. At web

breaks, the heating capacity of the drying cylinders must be reduced to avoid overheating of

the cylinders. Minimizing the number of web breaks is a good way to improve the

performance of a paper machine.

The goal of the project summarized in this paper was to derive optimal heat reductions, so

that the cylinder temperatures are retained when the production is restarted after the web

break. The main purposes with the models are to predict how the dryer section can be

improved or to improve dryer section control. In this paper an introduction to the paper

drying process is first givenfollowed by a presentation of simulation models and validation

examples.

The paper web goes through a number of steps on its way through the paper machine

The paper machine starts with the head box where pulp is evenly distributed on a screen.

Next section is the wire section where the sheet is formed on a wire. The wire is permeable,

and lets the fibres stay and the water flow away. In the press section more water is removed

by presses. The pressing also consolidates the web structure. In the dryer section the

remaining water in the paper is removed by evaporation on steam heated cylinders. The

surface is treated with a sizing solution in the surface sizing. The solution is added to improve

certain physical properties of the web, such as surface strength and printing properties. In the


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calender the sheet runs through roll nips to smooth the surface. The final step is the upwind,

where the paper web is reeled up on a tambour.

From the press section, the paper web enters the dryer section with 5070% moisture

content. After the dryer section the desired moisture content is 210%. Evaporation of water

from the wet paper sheet is energy consuming. In the dryer section, many properties of the

final product are determined. If the drying is performed poorly, the paper produced may be

too moist. The opposite, too dry paper, is a smaller problem, but can also lead to production

difficulties. If the paper is dried unevenly, the result can be curl. At the start of the dryer

section, the moisture content is high and the steam pressure has to be low in the first cylinders

to prevent the web from sticking on the cylinders. The lower the moisture content is in the

web, the higher the steam pressure is. The highest steam pressure is held in the last drying

cylinders in the dryer section. The drying cylinders are not controlled one by one, but are

organized into drying groups.

A web break is when, during operation, the sheet suddenly tears apart and production

has to be restarted. Web breaks can be caused by web flutter, holes in the paper sheet or if the

sheet is too wet or too dry.During web breaks, the heating capacity of the drying cylinders

must be reduced to avoid overheating of the cylinders. In some paper machines the steam

pressure is reduced to a fixed level and in others the reduction is accomplished in a certain

relation to the steam pressure before the break.

Fig.3:-Temperature measuring equipment mounted at the cylinder.

The temperature sensor (Swema SWT 315) has to be a contact sensor due to the fact

that the drying cylinders are shiny and therefore reflect radiation from an infrared sensor.

Humidity in the air can also absorb infrared radiation of certain wave lengths. If an infrared

sensor is used, it is more likely that the temperature of the surrounding air is measured and

not the cylinder temperature.


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The aim of this project was to control the steam pressure of the drying cylinder in

such a way that the same drying properties are obtained after the web break as before. To

achieve this, the steam pressure must be reduced during web breaks since the large cooling

effect from the paper web is lost. The objective is to have the same cylinder temperature

after the web break as before. The cylinder temperature is not measurable and therefore the

steam pressures in the cylinders are used as control variables.

The presented control strategy was the result of the aim to guarantee paper quality and

increase paper production by improving the steam pressure control during web breaks. The

model, describing the relation between the steam pressure in the cylinder and the cylinder

temperature, was verified through experiments performed on the paper machine PM7 in the

M-real Husum mill. Experiments were performed both during normal operation and during

web breaks. The measured steam pressure was fed into the model and the resulting cylinder

temperature from the model was compared with the true cylinder temperature. The

experiments showed that the output from the model agreed very well with the true cylinder

temperature.Based on the model, a new control strategy to improve steam pressure control

during web breaks was acquired. The idea was to use the information from the digital signal

that tells whether the paper is on the cylinder or not. This signal is used to change the set

point of the steam pressure controllers when the web breaks, and when the web is back on

the cylinder after the break. The idea behind the compensator was to obtain an optimal

cylinder temperature during the web break, so that the desired moisture content of the paper

is obtained as quickly as possible after the break.


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Title: - Energy assessment of Paper Machines

Author: -Naveen Bhutani, Carl-Fredrik Lindberg, Kevin Starr, Robert Horton.

Available: - 14 June 2012.

In this paper energy assessment is done by quantifying energy flows, benchmarkingenergy users, data mining and steam sensitivity analysis and by experiments and additional

measurements at the paper machine.There is a large value in making Pulp and Paper mills

more energy efficient. ABB has developed an energy assessment service where opportunities

to save energy in the paper machine are identified.

Paper machines consume a large amount of energy and in most cases large savings are

possible. An approximate overview of the dryer section of a paper machine is presented in

Fig. 1. The energy flows in the paper machine in the form of steam, condensate, air, water

streams and paper. The paper is dried when it travels on the steam heated cylinders. The

moisture in the paper is ventilated away and heat is recovered from exhaust air by air-air heat

exchangers and transferred to the inlet air, which is partly heated further in a steam-air heat

exchanger. The air to the machine hall is also heated in air-air exchanger and steam-air

exchanger. The condensate from steam heated cylinders is flashed in a condensate tank. Most

of the flash steam is recovered by thermo-compressors and recirculated back to steam

cylinders whereas the remaining flash steam goes to the condenser. The condenser is water

cooled and produces warm water by absorbing heat from flash steam. Some paper machines

also use steam box which makes pressing more efficient at the expense of steam

consumption.

Fig. 4. Schematic of paper dryer section of a paper machine


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The challenge is to find where energy is wasted and savings are possible. Measuring

and improving energy performance is of course not a new idea. They have found that the

pocket air ventilation, hood balance and dew point have significant influence of paper

machine energy efficiency.One of the important findings was, more than 10% of the total

steam energy was going to the condenser, which indicates that the excess flash steam was lost

to condenser due to poor steam control. One contributor to the large steam flow to the

condenser was inefficient thermo-compressors.A typical thermogram of dryer cylinders in

the end of the paper machine is presented in Fig.2, where the maximum and minimum

temperatures are given along the cyan lines in the image on the left. After investigation, only

minor problems were found with steam heated cylinders. For example one of the cylinders

was cooler in the end, and another cylinder was dirty which caused stripes in the thermogram

of the cylinder.The dryer cylinders are very shiny and sometimes it is possible that one gets

the temperature of the reflected object than the steam cylinder itself if the thermal camera is

not placed or mounted correctly.

Fig.5:-Thermogram of dryer cylinders

The thermograms were useful to detect temperature gradients along a cylinder and

temperature differences between different cylinders that could be used to detect of poorly

working cylinders. Though, it was difficult to trust the measured absolute values of

cylinders surface temperatures completely due to their sensitivity to emissivity factor, the

relative values for measured temperatures using same emissivity in all thermograms proved

to be useful.


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Fig. 6:- Thermogram and normal photo of hood.

A thermogram and normal photo of a section of the hood is shown in Fig.3. It can be

seen that the outside surface temperature of hood above the door is higher than surrounding,

which signifies the leakage of hot air from the hood. Therefore, the sealing of heat leak would

save energy and reduce the humidity in the machine hall. The need for ventilation in the

machine hall will also reduce if there is less leakage of moist air from hood to machine hall,

signifying steam savings for heating of the machine hall air.

ABBs recently developed paper machine steam energy fingerprint (audit) solution is

suitable for evaluation of steam cycle of the paper machine. By quantifying, benchmarking

and data mining, the steam supply, use and inefficiency can be measured. If the loss of

energy is beyond specifications, then the poor operating performance can be identified and

target solutions can be applied.

In this paper an investigation of the dryer section of a paper machine has been done

and the potential steam savings of 10-15% are possible by reducing process variations,

optimizing control set points for steam dryers groups, repairing and/or improving operation

of thermo-compressors, optimizing steam box pressure, seal leaks of hoods etc.


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Title: -Thermodynamic simulation of dryer section heat recovery in paper machines.

Author: -L. Sivill, P. Ahtila, M. Taimisto.Available: -10 September 2004.

In this paper, the simulation program is compared with measurements from three

paper machines. Furthermore, practical guidelines are presented for the improvement of

dryer section heat recovery based on conclusions from simulated examples.Modern paper

machines are equipped with heat recovery systems that are able to recover over 50% of the

energy used by the paper machine. The recovered heat is used for the heating of dryer

section supply air, process water and machine hall ventilation. Today, the structure of new

heat recovery installations is optimized with sophisticated algorithms to match the design

point of the paper machine.The heat recovery system of a paper machine is basically a heat

exchanger network that conveys energy from the humid exhaust air of the paper machine

dryer section to different process streams.The humid exhaust air from the dryer hood is

first led to conventional heat recovery (CHR) units, which recover heat to the dry supply air

going into the hood. After this, heat is recovered in aqua heat recovery (AHR) units to the

circulation water of machine hall ventilation process water, white water and/or wire pit

water, depending on the structure of the heat recovery system. Hence the fundamental

purpose of the dryer section heat recovery is to return part of the energy used by the paper

machine back into use in a profitable way. The exhaust air never becomes completely

saturated except for the thin boundary layer that develops on the surface of the heat

exchanger. Modeling of heat transfer from humid air requires the determination of the

surface temperature and the dew point throughout the whole heat exchanger.

The purpose of dryer section heat recovery is to decrease the energy use of a paper

machine as economically as possible. This includes providing the optimal structure of heat

recovery as well as efficient operation conditions for the system. In reality, there is no

guarantee that an installed heat recovery system will operate efficiently, since the original

design parameters may be appropriate only for a short period of time. After all, the main

purpose of a paper machine is to produce paper; the continuous effort towards a higher

production capacity does not automatically mean that energy economy is taken into

account. As a rule, energy efficiency can be improved for as long as it is financially

profitable and the changes do not compromise the production or cause problems to process

control and safety.Then again, running a process with high efficiency is more important

than getting the data right to the last digit.


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Title: -Design of robust heat recovery systems in paper machines.

Author: -Frank Pettersson , Jarmo Soderman.

Available: -9 June 2007.

The heat recovery system (HRS) is a vital part in a paper machine when it comes to

the overall energy economy in papermaking. For a typical newsprint machine more than 60%

of the exhaust energy from the dryer section can be recovered, resulting typically in a regain

of about 30MW.The synthesis task of a HRS is a decision process where the target is on the

one hand to achieve maximal energy recovery and on the other hand to obtain it with minimal

investment costs.

A modern paper machine may have a yearly production of 350,000 tonnes of paper and

a machine speed up to 2000 m/min. The papermaking process is highly energy consuming.

For manufacturing 1 ton of newsprint about 600 kWh electricity and 1500 kWh heat energy

are required. Almost all the heat energy is used in the drying section. Drying of the paper web

from about 3550% dry content to about 90% dry content is performed in the dryer section of

the paper machine where cylinders are heated with low pressure stream. For removal of

moisture, supply air at 95 C is blown into the paper hood resulting in an exhaust air flow

from the hood with a moisture content of about 100170 gH2O/kg dry air at a temperature of

8090 C. Almost all heat energy used in the process can be found in the exhaust air and it is

thus very suitable for attempts to recover the heat. The main target with heat recovery is

naturally considerable cost savings.

Fig.7:- Heat Recovery systems.


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The recovered heat can be used to heat a variety of streams. It can be transferred to the

circulation water heating the machine room ventilation air, to process water and to the

heating of supply air to the dryer section.The moist exhaust air from the hood is removed at

three different locations.

All heat exchangers are considered to be of counter current type and the minimum

required heat exchanger area for a given heat transfer is thus calculated using

Where Q is the heat load for the current heat exchanger,

U is the overall heat transfer coefficient and

TLM is the logarithmic mean temperature difference.


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Conclusion:-


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References:-1)Numerical and experimental investigation of paper drying: Heat and mass transfer with

phase change in porous media.

T. Lu, S.Q. Shen., online 12 January 2007.

2) A study of the spontaneous air flow through a moving porous medium.Jianyao Moua, G. Randall Straleyb, Xiaodong Wanga, 6 March 2003.

3) Heat and mass transfer in multicylinder drying, Part I. Analysis of machine data.Lars Nilsson., 6 May 2004.

4) Heat and mass transfer in multicylinder drying Part II. Analysis of internal and externaltransport resistances.

Lars Nilsson, 10 May 2004.

5) Cross-directional control of sheet and film processes.Jeremy G. Van Antwerp, Andrew P. Featherstone, Richard D. Braatz, Babatunde A.

Ogunnaike., 19 July 2006.

6) Improved web break strategy using a new approach for steam pressure control in papermachines.

Jenny Ekvalla, Tore Hagglund, 7 March 2008.

7) Energy assessment of Paper MachinesNaveen Bhutani, Carl-Fredrik Lindberg, Kevin Starr, Robert Horton., 14 June 2012.

8) Thermodynamic simulation of dryer section heat recovery in paper machines.

L. Sivill, P. Ahtila, M. Taimisto, 10 September 2004.

9) Design of robust heat recovery systems in paper machines.

Frank Pettersson, Jarmo Soderman, 9 June 2007.

10) Kuvalekar D. Reducing Specific Steam Consumption through Automation in Steam

Systems, Proceedings of PAPAEREX 2007, New Delhi, India, December 7-9, 2007.

11) Sivill L. and Ahtila P. Energy efficiency improvement of dryer section heat recovery

systems in paper machinesA case study.

Applied Thermal Engineering, 2009; 29, p. 3663-3668.

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