Operational Faults, Troubleshooting Measures, and Process Optimization of Closed-Loop Ventilation Hoods in Papermaking

The enclosed hood of the paper machine dryer section is a core component of the drying system, responsible for isolating internal and external airflows, balancing cylinder temperature and humidity, collecting moist, hot exhaust gases, and supporting waste heat recovery and utilization. It It directly affects the steam energy consumption of the production line, the uniformity of paper web drying, the stability of breakage, and the workshop operating environment.

During production operations, issues such as pervasive white mist, condensation inside the hood, elevated energy consumption, and uneven moisture distribution in the paper web are largely attributable to an overall imbalance in the operating conditions of the enclosed hood system. Drawing on frontline papermaking operation and maintenance experience, this paper identifies several common operational phenomena, their potential root causes, and indicative process‑optimization strategies, offering technical guidance for equipment commissioning and corrective maintenance at the mill.

I. Operational Condition Optimization of the Enclosed Hood System 

1.  Sealed Condensation on the hood top plate and internal dripping 
Potential contributing factors: aging of the hood insulation structure and declining airtightness at sealing points, leading to frequent mixing of hot and cold airflows; mismatch between exhaust airflow ratios and the paper machine’s evaporation load, resulting in the accumulation of moisture that cannot be promptly removed; and degradation of door‑seal components, which exacerbates the risk of air leakage and condensation. 
Reference optimization approach For this type of operating condition, the industry offers several viable optimization approaches. Improvements can be pursued across multiple dimensions, including insulation reinforcement, seal upgrades, airflow balancing, and air‑flow management. For example, aging insulation and sealing components can be inspected and replaced as needed, or system negative pressure can be fine‑tuned and fan operating parameters optimized to enhance exhaust and dehumidification performance. Enterprises can flexibly select solutions tailored to the specific conditions of their production lines. 

2.  Sealed Air hood leakage and significant white mist in the workshop. 
Potential causes: aging of the seal at wall panel joints and insufficient sealing of the access door; an improperly designed negative-pressure zone within the enclosure, which fails to establish a stable air-sealing effect, leading to the leakage of humid, hot air. 
Reference optimization approach : There is no standardized remediation approach for this type of issue; the optimization method can be flexibly selected based on the actual site conditions. Options include replacing sealing components and calibrating door‑stop limits to enhance overall airtightness, as well as fine‑tuning the negative‑pressure settings inside the enclosure and reinforcing the sealing of wall panel joints. Tailoring the corrective measures to specific needs can, to varying degrees, mitigate workshop white‑fogging and steam leakage from the enclosure. 

3.  Sealed Vibration and abnormal operating noises of the hood housing 
Potential causes: loosening at structural connection points, insufficient stability of internal flow‑guiding components, duct resonance, and airflow impact—any of these factors can trigger abnormal noise and vibration in the housing. 
Reference optimization approach : Based on on-site abnormal noises and vibration sources, multiple remediation approaches can be considered. Structural stability can be enhanced by tightening structural fasteners and reinforcing flow‑guiding components; alternatively, pipe‑mounted vibration isolation devices can be added, and fan operating conditions can be optimized. These measures are tailored to the specific equipment operating conditions of each plant and are intended solely as references for operation and commissioning. 

4.  Sealed The hood lift door experiences sticking during opening and closing, with abnormal operation. 
Potential contributing factors—such as slurry buildup and jamming in the track, uneven wire rope tension, inadequate lubrication of the drive mechanism, and fluctuating limit‑switch signals—can all compromise the smooth operation of the gate. 
Reference optimization approach : Regarding abnormal gate‑opening and closing issues, several viable optimization measures are available for consideration. Equipment condition can be improved by clearing debris from the tracks, adjusting wire‑rope tension, performing regular maintenance on the drive mechanism, and calibrating limit switches; paper mills can flexibly tailor these measures to their specific equipment wear and tear.

II. Process Optimization of Supply and Exhaust Air Systems and Fan Systems 

1. Insufficient exhaust airflow and elevated humidity inside the hood 
Potential causes: fouling on the fan impeller, blockages in the ductwork, sluggish damper operation, and inadequate matching of variable-frequency drive parameters can all result in insufficient dehumidification performance. 
Reference optimization approach : Optimization can be pursued across multiple dimensions, including equipment cleaning, structural maintenance, and parameter tuning. This may involve removing dust and slurry buildup from fans and ductwork, inspecting and servicing damper operation, or recalibrating variable-frequency drive–based airflow parameters. These approaches can be implemented individually or in combination to meet the diverse exhaust and dehumidification requirements of different production lines; they are provided for technical reference only. 

2. Abnormal noise from the fan and elevated operating current 
Potential causes—such as impeller dynamic imbalance, bearing wear or insufficient lubrication, and excessive pipeline system resistance—can all lead to abnormal operating loads on the fan. 
Reference optimization approach : Based on the fan’s actual operating condition, refer to the corresponding optimization plan. Cleaning the impeller, maintaining or replacing bearings, and clearing the exhaust ductwork to reduce airflow resistance can all mitigate equipment malfunctions to varying degrees. There is no one-size-fits-all corrective approach; adjustments must be made in light of site-specific conditions. 

III. Optimization of the Temperature and Humidity Control System 

1. Temperature data bias and inaccurate temperature measurements 
Potential causes: sensor fouling, airflow disturbances at the installation location, and signal transmission fluctuations, all of which can lead to distorted temperature measurement data. 
Reference optimization approach : Within the industry, a variety of calibration methods are available for reference. Data accuracy can be enhanced by cleaning sensor probes, optimizing installation locations, and verifying instrument parameters, among other approaches. The specific adaptation plan should be determined in light of the equipment’s actual operating conditions. 

2. Offset of the zero-pressure surface on the hood and airflow turbulence 
Potential causes: uneven opening of the dampers on both sides, unbalanced fan performance, and an unreasonable internal flow‑guiding arrangement, leading to a shift in the positive–negative pressure zone. 
Reference optimization approach : Refer to methods such as fine-tuning the exhaust dampers on both sides, balancing the operating loads of the fans, and optimizing the internal flow‑guiding structure to stabilize operating conditions. The specific adjustment procedures may vary and should be flexibly adapted to the actual airflow conditions at the site. 

3. Dew point imbalance and localized, recurring condensation 
Potential causes: Mismatch between exhaust airflow and production load, fluctuations in supply air temperature, and variations in waste‑heat recovery efficiency can all lead to recurring condensation issues. 
Reference optimization approach It can flexibly adjust exhaust and supply air parameters in accordance with the paper machine speed and paper grade, and the waste heat recovery system can also be optimized during maintenance. These multiple control strategies can all help address relevant operational issues; they are provided solely as a reference for operation and commissioning.

IV. Optimization of Waste Heat Recovery System Performance 

1. Heat exchange efficiency declines, and energy-saving performance is reduced. 
Potential causes: Scaling and slurry buildup on the heat exchange surface, along with internal leakage due to inadequate valve sealing, lead to a reduced thermal energy recovery efficiency. 
Reference optimization approach : Consider establishing a periodic cleaning and maintenance regime, or conducting inspections and replacing sealing valves, as well as optimizing heat‑exchanger operating conditions. A variety of operational‑maintenance optimization measures can enhance equipment performance, and enterprises may flexibly select the most suitable approaches based on their own O&M frameworks. 

2. The heat exchanger pressure drop continues to rise. 
Potential cause: Fine fibers and impurities in the exhaust gas continuously adhere to the pipe walls, leading to a gradual increase in pipeline resistance. 
Reference optimization approach : Consider improving flow integrity through regular tube‑bundle cleaning, or alternatively, install an upstream debris‑capture device and optimize the exhaust‑air filtration system. Both approaches can reduce the likelihood of blockages at the source, catering to the varying operational and maintenance requirements of different plant sites.

V. The Impact of Air Hood Operating Conditions on Paper Web Quality and Directions for Optimization 

1. Uneven transverse drying of the paper web and significant moisture variation 
Possible approaches include adjusting the air‑volume distribution across zones, optimizing internal airflow patterns, clearing blockages in the supply‑air system, and reinforcing local seals, among others, to achieve a more uniform drying performance across the entire paper web and reduce transverse moisture variations. The specific solution should be tailored to the actual operating conditions of the production line. 

2. Frequent paper breaks in the drying section; edges of the paper are prone to cracking. 
There are numerous industry‑wide approaches to technological upgrades, such as optimizing air‑cushion sealing, balancing dry and wet airflows, and stabilizing the drying curve. These measures can effectively reduce paper web shrinkage variations and surface weaknesses, thereby lowering the likelihood of breaks in the dryer section; they are intended solely as references for operational optimization. 

3. Steam energy consumption is relatively high. 
By adopting multi‑dimensional measures—such as optimizing airtightness, upgrading waste‑heat recovery systems, and finely tuning exhaust‑air parameters—it is possible to minimize heat loss and reduce overall steam consumption. Each paper mill can select the most appropriate optimization strategies based on its specific energy‑consumption challenges.

VI. Principles Governing Core Parameter Regulation and Operation & Maintenance Recommendations 

Negative pressure inside the hood, supply‑air temperature, exhaust‑air moisture content, and the zero‑pressure position are the four key parameters of a closed hood. There is no fixed standard for adjusting these parameters; they must be flexibly tailored to the paper grade, machine speed, and ambient conditions. The following guidelines are intended solely as operational references: appropriately set negative pressure can reduce white‑fog condensation, while excessive levels may increase energy consumption; an optimal supply‑air temperature can accelerate drying, but too high a temperature can make the paper brittle; and carefully controlling the exhaust‑air moisture content helps balance energy savings with effective condensation prevention. For routine adjustments, it is recommended to adopt a single‑variable, fine‑tuning approach, allow ample time to observe operating conditions, and supplement this with periodic full‑point inspections, thereby ensuring the hood’s long‑term stable performance. 

About Us 

Hunan Zhengding Environment specializes in the research, development, and manufacturing of complete sets of paper‑making drying and ventilation equipment, with its main business being… Enclosed hood, Yankee hood, waste heat recovery system, plant ventilation, dust collection system, paper‑stabilizing air box, air deflector An energy‑saving ventilation and drying system for papermaking. Tailored to the specific width, speed, and paper grade of each machine, we offer customized enclosed hood solutions, turnkey installations for new lines, and energy‑efficiency upgrades for existing facilities. We provide a one‑stop service encompassing site surveys, engineering design, manufacturing, installation, and commissioning, helping paper mills maintain quality, reduce energy consumption, and boost operational efficiency. For condition diagnostics, parameter optimization, or equipment selection advice, please contact us anytime to receive a personalized solution.