Process Parameters Optimization for Energy Saving in Paper Machine Dryer Section

Due to high energy consumption in the Chinese paper industry, this study considers higher-energy efficiency for the multicylinder dryer section of paper machines. A common situation in the Chinese paper industry is that energy is consumed in extensive mode. In order to improve the energy efficiency of the paper machine dryer section, deeper analysis and optimization of process parameters are necessary.

A NLP optimization method is developed for integration of steam system and air system to reduce the steam consumption and decrease the loads of centrifugal blowers in the multicylinder dryer section of a paper machine. Equality constraints of the optimization model are extracted from different process modules based on material and energy balance. Inequality constraints are from the production capacity, operating condition, etc. Two illustrative examples are presented in this paper. The results show that the optimization model is adaptive and convenient for application. For a newsprint machine, less dry air and steam are used and the energy consumption can be reduced by about 8% in the dryer section. Applied on a linerboard machine which has surface sizing, the method can reduce the energy consumption by 5.6%.     

HOW TO INCREASE THE DRYER EFFICIENCY - LOSS PREVENTION ON A PAPER MACHINE

In order to reduce superfluous energy consumption, the dryer section of an open paper machine was investigated experimentally. The recorded data covered the energy - and mass balances of both the individual drums and the whole dryer section, the state characteristics of the dryer air and some characteristics of the product. In the constant rate period of evaporation the specific heat consumption shows the minimum between 100 1050C dryer surface temperature while the specific evaporation performance is in direct proportion to it. The extent of the increase in energy consumption and of the decrease in evaporation performance below the critical value of moisture content is also demonstrated. Additional possibilities of energy saving exist mainly in aeration and in the more efficient operation of the presses. Some of the results are the characteristics of the investigated machine. It is believed, however, that the results referring to the effect of dryer surface temperature and moisture content are of a general validity and can be applied to other systems as well.     

HOW TO INCREASE THE DRYER EFFICIENCY - LOSS PREVENTION ON A PAPER MACHINE

In order to reduce superfluous energy consumption, the dryer section of an open paper machine was investigated experimentally. The recorded data covered the energy - and mass balances of both the individual drums and the whole dryer section, the state characteristics of the dryer air and some characteristics of the product. In the constant rate period of evaporation the specific heat consumption shows the minimum between 100 1050C dryer surface temperature while the specific evaporation performance is in direct proportion to it. The extent of the increase in energy consumption and of the decrease in evaporation performance below the critical value of moisture content is also demonstrated. Additional possibilities of energy saving exist mainly in aeration and in the more efficient operation of the presses. Some of the results are the characteristics of the investigated machine. It is believed, however, that the results referring to the effect of dryer surface temperature and moisture content are of a general validity and can be applied to other systems as well.     

Effect of operating parameters on the drying performance of multicylinder paper machine dryer section

The drying performance of multicylinder dryer section in a paper machine was investigated under various operating parameters: Inlet paper solid content (48–50%), inlet paper temperature (45–50°C), supply air temperature (100–90°C), and exhaust air humidity (75–85?g H₂O/kg dry air). The variation in environmental conditions was also considered. In this study, an improved static model was utilized to study the influence of these operating parameters on paper drying. The model was constructed using sequential modeling approach based on the drying techniques of multicylinder dryer section of a paper machine. The calculated paper solid content leaving each paper drying module and energy use is in agreement with the measured results. The simulation results showed that higher paper solid content and temperature entering the dryer section, lower supply air temperature, and higher exhaust air humidity were favorable for drying performance within the studied range of these parameters.     

EFFECT OF BLOW BOXES ON EVAPORATION DURING CYLINDER CONTACT IN A PAPER MACHINE DRYER SECTION

In this paper an inexpensive configuration for a cylinder blow box (CBB) and its effect on the evaporation rate are described. The objective of this work was to determine the effect of the blow boxes on drying intensity on a paper machine. The pilot machine trials were simulated with a computer program. Based on these results two cases were simulated for a commercial paper machine with and without blow boxes on single cylinders. The results revealed that when using the blow boxes on single cylinders, the drying rate can be increased by up to 15%. The potential for using this kind of configuration is biggest at the beginning of a dryer section. A simple construction of blow boxes makes this technique useful especially in boosting the drying performance of older paper and board machines. The exhaust air from the boxes can be utilized in ventilation of dryer pockets.     

真空冷冻干燥机远红外测温系统

真空冷冻干燥机自动进出料系统对冻干机温度探头的摆放一直是该系统的重要问题之一,上海千山远东制药机械有限公司技术人员发明了一套冻干机红外线测温系统。来正真意义上的达到自动进出料系统无人化。并且该系统,可靠性好,性能优越。     

THE DEPENDENCE OF PAPER MACHINE DRYING DRYING CHARACTERISTIC ON THE MACHINE GEOMETRY

The effect of the dryer cylinder diameter on the dryer specific evaporation rate is examined theoretically. It is observed that, in the range of cylinder diameters applicable in practice, the dryer specific evaporation rate is nearly independent of the selected cylinder diameter when the dryer geometry remains unchanged. In practice, however, the dryer geometries have changed slightly according to the cylinder diameter.

TO clarify the effects of the various component factors pertaining to the dryer geometry, this paper presents a drying characteristic, i.e.. a curve showing the dependence of the drying rate on the condensing steam temperature. The drying characteristic is given in the form of a nomogram to facilitate the evaluation of the effect of the ratio between the free draw length and the cylinder diameter, and the wrapping angle, to the dryer specific evaporation rate. Further, by means of an example, the specific evaporation rates obtainable for machine geometries currently used by various machine manufacturers are compared.     

EFFECT OF BLOW BOXES ON EVAPORATION DURING CYLINDER CONTACT IN A PAPER MACHINE DRYER SECTION

ABSTRACT

In this paper an inexpensive configuration for a cylinder blow box (CBB) and its effect on the evaporation rate are described. The objective of this work was to determine the effect of the blow boxes on drying intensity on a paper machine. The pilot machine trials were simulated with a computer program. Based on these results two cases were simulated for a commercial paper machine with and without blow boxes on single cylinders. The results revealed that when using the blow boxes on single cylinders, the drying rate can be increased by up to 15%. The potential for using this kind of configuration is biggest at the beginning of a dryer section. A simple construction of blow boxes makes this technique useful especially in boosting the drying performance of older paper and board machines. The exhaust air from the boxes can be utilized in ventilation of dryer pockets.     

Comparison of Several Multi-Cylinder Paper Drying Simulation Models

Many models for simulation of paper drying in multi-cylinder dryer sections exist. In this work. three independently developed models are directly compared using the same reference data The models consired are the Texas A&M model, the Kuiosa model, and the VTT model. Predicted moisture contents plus cylinder and avenge web temperatures along the dryer section are presentcd for the different models. Predicted average evaporation rates during drying are also shown. Three major differences in the model details are highlighted. The effects of these differences on model accuracy evaluated by considering two different paper grades dried with two different machine geometries. This work is the first published direct comparison of different simulation models. The reference machine data provided can be used for comparison of these three models to other models.     

Enhancement of Drying Rate in Paper Machines with Multi-Functional Radial Jet Reattachment Blow Boxes — Theoretical Analysis

Multi-functional radial jet reattachment blow boxes deliver a dry air into the pockets of the dryer section of a paper machine by impinging directly onto the unsuppned sheet in the open diaw. The air flow also maintains or improves the sheet swbility.

The iadial jet reattachment blow box technology pmvides a significant enhancement in drying rates. The theoretical drying results are presented in terms of average drying rates, moisture and temperature pmfiles along the drying section with and without the presence of the multi-functional radial jet reaaachment blow boxes. The thcorclical results indicate that enhancements of drying rates within the range of 8% to 25% are feasible depending on ihe operating conditions and machine configuration.     

Comparison of Several Multi-Cylinder Paper Drying Simulation Models

ABSTRACT

Many models for simulation of paper drying in multi-cylinder dryer sections exist. In this work. three independently developed models are directly compared using the same reference data The models consired are the Texas A&M model, the Kuiosa model, and the VTT model. Predicted moisture contents plus cylinder and avenge web temperatures along the dryer section are presentcd for the different models. Predicted average evaporation rates during drying are also shown. Three major differences in the model details are highlighted. The effects of these differences on model accuracy evaluated by considering two different paper grades dried with two different machine geometries. This work is the first published direct comparison of different simulation models. The reference machine data provided can be used for comparison of these three models to other models.     

THE DEPENDENCE OF PAPER MACHINE DRYING DRYING CHARACTERISTIC ON THE MACHINE GEOMETRY

ABSTRACT

The effect of the dryer cylinder diameter on the dryer specific evaporation rate is examined theoretically. It is observed that, in the range of cylinder diameters applicable in practice, the dryer specific evaporation rate is nearly independent of the selected cylinder diameter when the dryer geometry remains unchanged. In practice, however, the dryer geometries have changed slightly according to the cylinder diameter.

TO clarify the effects of the various component factors pertaining to the dryer geometry, this paper presents a drying characteristic, i.e.. a curve showing the dependence of the drying rate on the condensing steam temperature. The drying characteristic is given in the form of a nomogram to facilitate the evaluation of the effect of the ratio between the free draw length and the cylinder diameter, and the wrapping angle, to the dryer specific evaporation rate. Further, by means of an example, the specific evaporation rates obtainable for machine geometries currently used by various machine manufacturers are compared.     

Energy system diagnosis of paper-drying process,Part 1: Energy performance assessment

Paper drying is a highly energy-intensive and complicated multivariate process. The dryer section plays an important role in the energy consumption of a paper machine, especially of thermal energy. A comprehensive method for assessing the energy performance of the dryer section was investigated in this study to improve energy efficiency. This method was divided into three component processes: energy and evaporation load audit, field test and observation, and energy flow analysis and energy efficiency estimation. In a case study, we found that the method could, in addition to analyzing the key factors that restrict drying efficiency, also depict the details of energy consumption clearly. At the same time, several significant energy-saving measures were suggested to improve the energy efficiency of the paper-drying process.     

THE INFLUENCE OF VACUUM ON DRYING OF PAPER

It is well known in the drying of paper that it is possible reduce the size of the dryer section and/or increase the drying capacity by using vacuum. Furthermore a smaller dryer section contributes to a decrease in the energy losses. However, the use of Minton vacuum dryers in the late 20's was never really successful. Especially with increasing machine speeds maintenance became a problem.

Vacuum drying leads to an improvement in the optical pro- perties of papers made from mechanical pulps. Some physical properties such as softness and porosity may also be improved. When the paper is pressed towards the hot surface under me- chanical pressure during vacuum drying a gain in mechanical properties can be achieved.

In the present investigation, the influence of heat transfer between the web and the hot surface as well as mechanical com-pression of the sheet during vacuum drying have been avoided by using an IR heat source. The results show that the main effect of vacuum is a reduced evaporation temperature. This allows the drying to reach its maximum rate faster. The lower temperature level during vacuum drying also makes cheaper energy sources avilable.     

Energy system diagnosis of paper-drying process,Part 2: A model-based estimation of energy-saving potentials

The pulp and paper sector is the fourth largest industrial sector in terms of energy use in the world. Of the numerous processes involved in paper-making by a paper machine, the dryer section is the process that consumes the largest amount of energy. A model-based method for estimating energy-saving potentials of the dryer section was put forward in the present study. It was done by four steps: establishing a mathematical model about energy consumption, determining the model parameters, benchmarking the drying performance to obtain the corresponding energy-saving measures, and estimating the energy-saving potentials by using the mathematical model. In a case study, a multi-cylinder dryer section was selected to illustrate the method. After a fundamental field test and observation, several operating problems that restricted the energy performance of paper drying were found. And then several reasonable energy-saving measures were suggested to the operators. Finally, applying the mathematic model, it was found that 0.32 ton of steam will be saved when producing 1 ton of paper in recommended operating conditions. With the designed capacity of 200,000 tons/year, the annual steam-savings will be 64,000 tons. Generally, the price of steam is 130–150 Chinese Yuan (about US$21–24) in China, and the annual economic benefits will be 8.32–9.60 million Chinese Yuan (about US$1.344–1.536 million).     

Enhancement of Drying Rate in Paper Machines with Multi-Functional Radial Jet Reattachment Blow Boxes — Theoretical Analysis

ABSTRACT

Multi-functional radial jet reattachment blow boxes deliver a dry air into the pockets of the dryer section of a paper machine by impinging directly onto the unsuppned sheet in the open diaw. The air flow also maintains or improves the sheet swbility.

The iadial jet reattachment blow box technology pmvides a significant enhancement in drying rates. The theoretical drying results are presented in terms of average drying rates, moisture and temperature pmfiles along the drying section with and without the presence of the multi-functional radial jet reaaachment blow boxes. The thcorclical results indicate that enhancements of drying rates within the range of 8% to 25% are feasible depending on ihe operating conditions and machine configuration.     

PAPER DRYING: A STRATEGY FOR HIGHER MACHINE SPEED. II. IMPINGEMENT AIR DRYING FOR HYBRID DRYER SECTIONS

For printing and heavier grades, combining cylinder and impingement air drying into a multiple technique dryer section can enable higher productivity through higher machine speed. The large differences in local moisture content and temperature across the sheet which develop quickly under high intensity impingement drying provide the potential for reducing drying time by sheet reversal between impingement drying cylinders. This advantage was determined experimentally under low intensity impingement drying conditions. Use of the micro-scale based McGill dryer simulator for determining the advantage from sheet reversal between impingement drying cylinders was demonstrated for both laboratory and industrial impingement drying intensities. For completing the drying of 205 g/m² linerboard from 0.3 to 0.5 kg/kg dry under 400°C air jets of Re 20000, drying time is about 30% less with sheet reversal between two impingement drying cylinders than for a single, larger diameter cylinder. This extensively validated dryer simulator enables determining advantageous design specifications and operating conditions for hybrid dryer sections involving combinations of cylinder and impingement air drying, a concept with potential to become common industrial practice.     

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

A mathematical model describing the heat and mass transfer in the dryer section of a paper machine has been applied to the production data from four paper machines. Model predictions for the machine speed are compared to actual machine speeds for a total of 163 data sets. The mathematical model assumes that the temperature and moisture content remain homogeneous in the thickness direction of the sheet. For three paper machines producing paper with basis weights ranging from 0.056 to 0.159 kg d.s./m² the model predictions are adequate. For the paper machine producing the heaviest grades with basis weights ranging from 0.189 to 0.390 kg d.s./m² the model predictions are flawed by a systematic error. For low machine velocities/high basis weights the machine velocity is over-predicted and for high machine velocities/low basis weights the machine velocity is under-predicted. This systematic error is caused by the assumption of homogeneous moisture content and temperature within the sheet being severely in error for thick sheets.     

Steady-State Modeling of Multi-Cylinder Dryers in a Corrugating Paper Machine

In this study, a steady-state model was developed to describe the paper drying process and to analyze pocket dryer conditions for a multi-cylinder fluting paper machine in Iran's Mazandaran Wood and Paper Industries. The machine has 35 cylinders grouped in three drying groups and the cylinders are heated from the inside by steam. The model is based on the mass and energy balance relationships written for fiber, air, and water in the drying section. In this research, the heat of sorption and its variations with paper temperature and humidity changes have been taken into account. Temperature and moisture variation of the paper web and cylinder surface temperature in the machine direction were predicted by the proposed model. Also, temperature and humidity of air in the drying pockets and hood exhaust were estimated by the proposed model. Moreover, the model can predict the evaporation rate and specific drying rate with sufficient accuracy in comparison with the TAPPI standard. Finally, the main modeling parameters were compared with the available operating data and the effectiveness of the developed model was verified through validations.     

Fluxes and Patterns of Wall Deposits for Skim Milk in a Pilot-Scale Spray Dryer

The pattern of wall deposits in a pilot-scale spray dryer has been studied, using skim milk, by changing the flow rate to the nozzle and measuring the resultant deposition fluxes at different positions inside the dryer. The solids concentration was maintained at 30%. The deposition was measured at three locations of the conical section and in the cylindrical section of the spray dryer. Particle deposition can be either due to the inertia of the particles or turbulent diffusion, and it is not immediately obvious which of these mechanisms is dominant. Inertial deposition appeared to be present mainly at the bottom location of the conical section and was the largest amount in quantitative terms, being at least an order of magnitude larger compared with diffusion deposition, which seemed to be dominant on the side (cylindrical) walls of the spray dryer. In addition to the above observations, the deposition patterns in the conical section have been quantified. The relative deposition flux, in m^-2, which is the ratio of the deposition flux, in g m^-2 h^-1, to the solids flow rate into the dryer, in g h^-1, was between 0.04 and 0.09 m^-2 at a solids concentration of 8.8% and between 0.15 and 0.4 m^-2 at a solids concentration of 30%. The fused appearance of the microstructure in the wall deposits of skim milk powder, as seen in the Micro-CT study, suggests that re-entrainment of the wall deposits is unlikely.