Paper Dryer Control

Introduction

In the papermaking process, drying is an important step in which the remaining water in the wet paper web evaporates. This is performed by a dryer. The humidity control in the dryer is essential to maintaining high paper quality (e.g., strength, paper surface properties) and high heat energy efficiency. The ZR802G Direct in-situ Zirconia High-Temperature Humidity Analyzer requires no sampling system and provides stable operation in high-temperature environments.

Process

The pulp suspension is dispersed uniformly, dewatered, and pressed to produce wet paper, the moisture content of which is approximately 20 to 50%. The remaining water is removed by evaporation. This is achieved by passing the sheet through a steam-heated roll in a closed dryer. The water is evaporated by re-circulating hot (50 to 120°C), low-humidity air through the dryer. To maintain the specified humidity, humidity meters are installed at several locations in the dryer.

Features

• Increases the heat energy efficiency of the dryer in the papermaking process
• Ensures high paper quality
• Reduces operating costs

Product Recommendations

Sensor:     ZR22 Oxygen Detector
Analyzer:  ZR802 Oxygen analyzer

Calibration:

MC1      Single channel manual calibration unit
AC1      Single channel automatic calibration unit
IAC24   Integral automatic calibration unit

Field Data

Process Conditions
Measurement point:   Closed (semi-closed) hood or the exhaust duct
Temperature:              50 to 120°C

Notes on Installation

• The sensor is hot. To remove a possible ignition source, a dust protector should be used to prevent suspended paper dust from coming into contact with the sensor
• Since the process humidity is low, the humidity of the reference air greatly affects the accuracy. Clean, dry air such as instrument air should be used as the reference air. If such air is not available, a customized flow setting unit with a humidifier should be used.

Notes

• The humidity measurement system introduced here can also be used in dryers in the flour and starch-making processes.
• For more information contact the Yokogawa Analytical Marketing Department.