TIP 0404-50 Paper machine room ventilation guidelines

TIP 0404-50

ISSUED – 1998 REVISED – 2003 REVISED – 2009 REVISED – 2015

2015 TAPPI The information and data contained in this document were

prepared by a technical committee of the Association. The committee and the Association assume no liability or responsibility in connection with the use of such information or data, including but not limited to any liability under patent, copyright, or trade secret laws. The user is responsible for determining that this document is the most recent edition published.

TIP Category: Automatically Periodically Reviewed (Five-year review)

TAPPI

Paper machine room ventilation guidelines Scope This Technical Information Paper provides an overview of principles and guidelines for designing and optimizing paper machine room ventilation systems. Safety precautions Normal safety precautions should be taken when working around operating machinery, hot surfaces, and steam systems. Application note This Technical Information Paper provides general descriptions and guidelines for designing air systems and estimating airflow requirements for machine room ventilation systems. Engineers with experience in paper machine room air handling should be consulted for specific design work and to address specific operating problems. Calculations are presented in both English and SI units. Refer to Table 1 for English to metric conversions. Two sample calculations are included at end of the TIP; one for a linerboard paper machine and one for a copy grade paper machine. Ventilation principles Purpose and benefits Ventilation air is used to improve drying uniformity and capacity, improve the working environment, reduce maintenance of roof and building equipment, reduce product contamination, and extend process equipment life. The amount of air required to produce a ton of paper can be 75 tons or more, depending on the grade of paper. Ventilation air serves two primary purposes:

contain and remove water vapor, heat, and dust replace air removed in the drying process and by vacuum systems

Ventilation systems can also cause unsafe conditions and impact production if not designed, operated, and maintained properly. A well ventilated building has the following attributes:

good visibility (no fog) in the production areas no condensation on wall and ceiling surfaces

TIP 0404-50 Paper machine room ventilation guidelines / 2

comfort working conditions in operating areas no stagnant airflow areas controlled airflows in and out of the building for efficient paper drying and sheet handling energy efficiency

Contaminants The three major contaminants present in a paper machine environment are water vapor, heat, and dust. Water vapor Uncontained water vapor will spread throughout the building primarily by convective air flows and, to a lesser degree, by diffusion. Fog and condensation occur when the water partial pressure exceeds the equilibrium vapor pressure, which is dependent on the local temperature. The local temperature is a function of the heat gain or loss. Heat Papermaking is an energy intensive process. Typical process heat loads are listed as follows:

Area/Source Floor Level Heat

Btu/ton kW-h/tonne Stock Preparation

- Refiners Bleached Board: Corrugating:

Fine Paper: Linerboard: Publication:

Operating 73 900 37 000 88 000 51 700 59 100

19.6 9.8

23.4 13.7 15.7

- Cleaners (based on footprint) Operating 1 000 Btu/h/ft2 3.15 kW/m2 - Pumps & Piping Ground 20 000 5.3 Former & Press - Vacuum System Ground 37 000 9.8 - Pumps & Piping Ground 75 000 19.9 PM Drive - Forming & Press Operating 51 600 13.7 - Main Dryer Operating 18 500 4.9 - Size Press Operating 3 200 0.9 - After Dryer Operating 6 400 1.7 - Calender Operating 14 500 3.9 - Coater Operating 27 100 7.2 - Reel Operating 8 600 2.3 - Winder Operating 44 400 11.8

Dust Airborne dust in high concentrations is an occupational health concern and can become a fuel source for fires. The major sources of dust come from poor broke handling practices, sheet shedding doctor blades, and winder slitters. Sheet over-drying increases dusting. Air lances, air nozzles, and air hoses should be avoided in cleaning dusty areas because they can cause dust to become airborne. Dust prevention should be the primary focus, with cleaning and collection being the last steps.

TIP 0404-50 Paper machine room ventilation guidelines/ 3

Recommended levels Minimum and maximum levels for temperature, humidity, and dust are recommended based on location within the machine room:

Variable Location Minimum Maximum (above outdoor ambient)

Remarks

Temperature °F

Ground Floor Operating Floor – tending, wet end Operating Floor – tending, elsewhere Operating Floor – drive side Mezzanine Underside Roof

65 75 65 65 - -

≤ 10 ≤ 5 ≤ 5 ≤ 10 ≤ 20 ≤ 25

Humidity grains H2O/lbDA

Ground and Operating Floors Mezzanine Underside Roof

- - -

≤ 50 ≤ 100 ≤ 150

No fog or condensation

Dust mg/m3

Total (all airborne particles) Respirable (airborne particles <10 μm)

- -

15 (including ambient) 5 (including ambient)

Factors affecting ventilation performance The amount of ventilation air required is a function of a number of factors, including the following:

Factor Impact on Building Ventilation Production Rate Higher production rates have higher evaporation rates and, correspondingly, require

more air Grade of Paper Lighter grades are more susceptible to air drafts Machine Speed Higher heat and mass transfer with increased machine speed Type of Former Top wire and gap formers require higher exhaust rates than fourdrinier formers Stock Temperature Increase mass transfer rate with increase in temperature Type and Condition of Dryer Hood Open hood requires more exhaust air than a closed hood Climate Colder climates require higher building air balance

Warmer climates require higher ventilation rates during the summer Building Geometry Air follows the path of least resistance leading to short-circuiting of air Equipment Layout Multiple machines in the same building are more difficult to ventilate than single-

machine rooms Building Construction Building pressure is dependent on building tightness

Increased risk of condensation with less wall and roof insulation

Air movement Building air movement is a function of the air pressure, momentum, and density. The velocity of air discharged from a one-foot diameter opening drops to ten percent of its initial velocity within thirty feet from the opening. Stack effect causes cool and dry air to enter the building at the ground floor level as warm, moist (less dense) air rises to the underside of the roof, resulting in a vertical pressure difference with respect to the building exterior. With equal supply and exhaust flows, a neutral pressure level, or “null point”, would occur at or below the mezzanine floor level. Above the null point, air exfiltrate out (positive pressure) of the building and conversely infiltrate (negative pressure) into the building below the null point. The dryer section hoods are greatly affected by stack effect. Increasing the hood exhaust or reducing the supply flow rates raises the null point. Decreasing exhaust or increasing supply flows lowers the null point. Opening doors below the null point introduces more air into the enclosure, which is comparable to increasing the supply flow and in turn lowering the null point. Opening a felt-loading door, above the null point, is equivalent to increasing the exhaust flow rate and raising the null point, even though hot and humid air would be “dumped” into the machine room.


Ventilation methods (3,4) Four primary methods of ventilation are: mixed ventilation (dilution), unidirectional ventilation (piston airflow), displacement ventilation (passive thermal displacement), and localized ventilation (spot cooling). Displacement ventilation is the recommended method for paper machine building ventilation, with local ventilation applied to isolated areas. General guidelines

1. Capture heat and water vapor as close to its source as possible because it will require less exhaust air flow than diluting it later.

2. Minimize the amount of air exhausted to reduce energy costs. 3. Move air from areas of low heat and water vapor concentrations to areas of high heat and water vapor

concentrations: dry-end-to-wet-end and tending-side-to-drive-side. Introduce air into the building such that it removes as much heat and water vapor as practical before being exhausted.

4. A balance of supply and exhaust systems is required for either any ventilation system to function as designed.

5. General ventilation should primarily be used for comfort control, with water vapor control usually a secondary consideration. Dilution ventilation reduces overall water vapor concentration and temperature.

6. Use make-up air for personnel ventilation only. 7. Supply air should have sufficient volume and heat to prevent condensate and fog from forming. 8. Displace heat and water vapor from operating personnel zones with large quantities of make-up air.

Distribute air directly to work zone (below 10 feet) to provide effective dilution ventilation. Avoid high velocity discharges, which entrain warm and humid air streams.

9. Care should be taken to avoid unintentional short-circuiting. 10. The exhaust discharge, whether local or general, should be directed so as to reduce the possibility of

reentry. Exhaust discharges should be located away from windows and air intakes. 11. Avoid locating ventilation ducts in the upper building levels unless insulated. 12. Perform regular maintenance on ventilation equipment and systems to ensure optimum performance. 13. Test ventilation systems periodically to ensure they continue to operate as designed.

System description and dimensioning Exhaust systems The first priority of a good ventilation system is to capture heat and vapor at the source. Paper machine room ventilation systems should include:

Forming section exhaust

Dryer section hood exhaust

Saveall exhaust

Pulper exhaust

Building exhaust o Wet end false ceiling o Size press and coater false ceilings o Roof exhaust

Forming section exhaust Forming section exhaust systems contain and exhaust water vapor from between and below the forming wire.


The former and showers should be shielded, as much as possible, and vapor should be exhausted from the drive side. Make-up air supplied to the tending aisle, opposite the forming and press sections, promotes a tending-side-to-drive-side airflow and increases the effectiveness of forming section exhaust systems. Fourdrinier formers Air is exhausted from four areas along the length of a fourdrinier forming section:

Inside wire loop – between wire and saveall Inside wire loop – below saveall Wire pit Couch pit

Recommended flow rates (ft3/min or m3/s) are calculated on the basis of a flow factor times machine design speed (ft/min or m/s) times the trim width (inches or meters) based on a stock temperature of 120°F (49°C):

1200016.67

vt

V Cw

(English Units)

5.664.56

vt

V Cw

(SI Units)

where

V

= volumetric exhaust rate, ft3/min or m3/s v = machine speed, ft/min or m/s w = reel trim width, in or m

tC = stock temperature correction, dimensionless

= 1.0 for 120°F (49°C) = 1.3 for 130°F (54.5°C) = 1.8 for 140°F (60°C) Top wires and gap formers Typical exhaust points from a top wire forming section are from inside the wire loop, and after the high-pressure cleaning shower. Typical pickup points on gap formers are the headbox area, inner and outer wire loops, and after high-pressure showers. Many of the new installations include tending and drive side shields, eliminating much of the water vapor. Machinery builders typically provide ventilation air pickup points and recommended exhaust volumes for new and rebuilt formers. Recommended flow rates (ft3/min or m3/s) are as follows: Top wire former:

v6000

24t

wV C (English Units)

v2.83

6.56t

wV C (SI Units)


Gap former:

0.11vt

V Cw (English Units)

0.40vt

V Cw (SI Units)

Exhaust air from the forming section is often nearly saturated with water vapor. Exhaust points near high-pressure showers or with high pick-up velocity entrain water droplets and fiber in the air stream, which are then removed through a mist eliminator prior to the exhaust fan. Mist eliminators vary in design from drop-out chambers and eliminator blades, to cyclone and swirl tubes. Care is required at the discharge point to avoid recirculating vapor back into air intakes or exhausting air over roadways. No system actually “eliminates” mist at the discharge point; rather, it removes it from the forming section. The water/fiber separator removes most particulate and water droplets from the air stream, but air that is expelled to the atmosphere is still saturated with water, which appears as mist when the mixture is discharged into cooler outside air. Introducing heated air into the exhaust stream prior to discharge reduces the fog formation associated with cold weather operation. Vacuum pump/blower exhaust Exhaust streams from blowers and compressors are hot and humid and contain a lot of energy. Use indirect heat exchangers to recover heat from vacuum blower exhaust, if justified. Vacuum flow rates depend on the paper and board grades being produced and the machine configuration, and are typically specified by the machine supplier. TIP 0502-01 “Paper machine vacuum selection factors” (5) and TIP 0404-27 “Press fabric dewatering and conditioning-suction box (Uhle box) design and vacuum requirements” (6) provide guidelines for sizing vacuum systems. Typical vacuum flow rates range from 90 to 150 scfm/in trim (1.67 to 2.79 sm3/s/m) from the forming and press sections. Dryer section hood and associated air systems Refer to TIP 0404-24 “Recommended operation of dryer section hood air systems” (7) and TIP 0404-17 “Recommended minimum dryer pocket air requirements” (8) for exhaust and pocket ventilation system description, guidelines for operation, and dimensioning. One of the largest sources of heat and water vapor in the machine room is from the dryer section. The heat and water vapor load is particularly high when hood doors are left open, especially if hood exhaust is not properly designed, dimensioned, and functioning. The front lift, rear sliding, and basement enclosure doors must be kept closed for the ventilation system to be effective in capturing and exhausting water vapor. Refer to TIP 0404-24 for specific requirements for sizing hood exhaust and supply systems for the various hood construction types. Pulper exhaust Several pulper suppliers provide exhaust pickup points with recommended air volumes and static pressures. Typical exhaust rates per trim width per location are as follows:

Location Flow Rate ft3/min/ft m3/s/m Press Pit (1-48” wide slot) 720 1.11 Size Press (1-40” slot) 600 0.93 Reel (2 slots - 12” & 36”) 720 + Trim Conveying 1.11 + Trim Conveying Winder (1-36” slot) 540 0.84


Additional exhaust is required if a trim conveying system discharges into the pulper. The preferred design is a cross-machine header incorporated into pulper design with multiple inlet points to minimize broke carryover. Access doors are required in the duct approximately every 20 feet (6 m) starting at the connection to the pulper. Saveall exhaust Wet end savealls and broke thickeners are typically covered by a hood and exhausted to maintain an inflow of air when the inspection doors or covers are open. Most modern disc filters and broke thickeners are furnished with tight fitting hoods, which require a vent to atmosphere or a minimum exhaust rate such as 2500 ft3/min (1.2 m3/s). Open hoods require a considerably higher exhaust rate and are designed with an inflow velocity around the perimeter of 150 ft/min (0.75 m/s). Building exhaust Building exhaust systems remove the heat and water vapor that cannot be captured at the source of origin. Wet end exhaust rates for water vapor removal, in most cases, exceed the requirements for heat removal from the forming and press sections. Supplemental exhaust is required from stock preparation and the building dry end for temperature control. Wet end false ceiling and exhaust A wet end false ceiling and ducted fans exhaust air and water vapor from above the forming and press sections. A false ceiling should extend in the machine direction from the headbox to the furthest point of the press section, typically the press overhang. In the cross machine direction, the false ceiling should extend from the drive side crane column to beyond the tending side of the wire with a side curtain down, as a minimum, to the mezzanine. Recommended flow rates are calculated from the product of exhaust rate per area, machine design speed (ft/min or m/min), and trim width (ft or m) based on a stock temperature of 120°F (49°C):

v 10

100t w

V AC C nDw EC

where

V

= volumetric exhaust rate, ft3/min or m3/s v = machine speed, ft/min or m/s A = area, ft2 or m2 reel trim width x distance from headbox to dryer section, including press overhang

tC = stock temperature correction, dimensionless

= 1.0 for 120°F (49°C) = 1.38 for 130°F (54.5°C) = 1.87 for 140°F (60°C)

wC = wire surface area adjustment, dimensionless

= 1.00 for fourdrinier = 1.25 for top former or gap former C = Conversion factor = 1.0 for English units = 196.75 for SI units


D = steam box and lazy steam shower adjustment = 2,000 ft3/min/ft = 3.1 m3/s/m E = exhaust correction, dimensionless = 1.00, rear curtain in place = 1.25, no rear curtain n = number of steam boxes and/or lazy steam showers w = reel trim width, ft or m

Size press and coater false ceiling and exhaust Dryer hood breaks for breaker stacks, size presses, etc., are sources of vapor to spill into the machine room. These areas are ventilated similarly to the forming and press section, with false ceilings with drive side exhaust. Recommended flow rates are calculated from the product of the exhaust rate per area, the machine speed (ft/min or m/min), and trim width (ft or m) based on a surface temperature of 150°F (66°C):

0.0242vV B A

where Ѷ = volumetric exhaust rate, ft3/min or m3/s v = machine speed, ft/min or m/s A = area, ft2 or m2 reel trim width x distance between main and after hoods, or length of coater section B = flow constant = 14.8 ft3/min/ft2 = 0.0752 m3/s/m2

Supplemental roof exhaust High-level roof exhaust is required to remove any vapor that escapes from local exhaust systems and from areas with high thermal loads, such as stock preparation, coater, winder, and roll wrap areas. The exhaust rate is based on the ground and operating floor heat loads with the majority being from motors and piping. The heat loads listed under “Heat Contaminants” are typical and can be used as a starting point. The minimum cold weather exhaust rate is calculated on the basis of removing the total process heat gain with a 25°F (14°C) temperature differential. The minimum flow rate should equal or be less than the total process exhaust rate including the wet end false ceiling exhaust. Additional roof exhaust in stock preparation and the building dry end is added to meet the minimum exhaust rate. An added minimum of twenty-five percent of the wet end false exhaust rate should be drawn from the truss space to remove vapor not captured by the false ceiling and forming section exhaust systems. This is typically achieved by adjusting the stock preparation roof exhaust rate. Similarly, an additional ten percent of the dryer section exhaust should be drawn from the truss area to remove vapor escaping from dryer section hood(s) when the doors are periodically opened. Here, the dry end exhaust rate is adjusted to meet the vapor load criteria. Exhaust should be located over the drive aisle from both the wet end and dry end roof areas.


Summer roof exhaust In most cases, it is desirable to increase the ventilation rate by adding roof exhaust fans that operate only in the summer months. Special attention should be given to wet end truck doors that are left open during the summer and affect dry-end-to-wet-end airflow patterns. Exhaust alone can seldom eliminate hot working conditions on the machine room floor. Use of forced summer ventilation is preferred practice in warm-climate mills. The minimum summer exhaust rate is calculated on the basis of reducing the temperature rise to 10°F (6°C) of the ground floor heat gain since most of the heat will be drawn up through the operating floor. Additional fans are added in the stock preparation, coater section, and building dry end to offset the heat loads. Supplemental air supply, such as wall fans or air make-up units, should be added to maintain a minimum balance of 75%. Depending on the airflow patterns, the powered supply air flow rate can be as low as 50% of the warm weather exhaust rate. Supply systems Make-up air Exhausting air without replacing it with heated make-up air draws cold air, in the winter, through doorways and openings, reduces building air temperature, causing fog and condensation in the forming and press sections. Fog and condensation are less severe during warmer weather and are replaced by hot working conditions along the operating floor. Note that absence of visible fog does not imply absence of high humidity conditions. Most modern ventilation systems are designed with a 100 to 105% winter air balance. Displacement ventilation introduces cool (ambient in summer) air at low levels and displaces contaminants vertically using the buoyancy forces. Supplying fresh, low-humidity air along the tending side within eight feet or 2.5 meters of the operating floor provides operator comfort before picking up heat and humidity as it moves up and across the machine toward exhaust points. Distribution All exhaust should be concentrated on the drive side of the machine room, with the majority located at the wet end of the building. Supply air distribution should be concentrated on the tending aisle at operating floor level creating two basic airflows through the building: tending side to drive side, and dry end to wet end. Guidelines for supply air distribution are as follows:

Floor Level Total Tending Side Drive Side Remarks Mezzanine 0-to-5% - 0-to-5% Spot cooling Operating 70-to-80% 50-to-60% 10-to-20% Drive motor cooling supplies air to drive side Ground 20-to-30% 10-to-20% 5-to-10%

Infiltration air Locations of openings into the building and through the operating floor are important. Infiltration air can adversely affect an otherwise theoretically correct building air balance. Some systems have been designed with strong dry-end-to-wet-end airflows, but actually result in air exfiltrating at the dry end and infiltrating at the wet end.


Heating coils Steam coils have traditionally been used to heat supply air. Glycol/water systems are preferred because of reduced maintenance, eliminating freezing problems, and opportunities to use low-grade process heat. Other supply systems use gas-fired heaters, but emission restrictions and operating costs have limited their use. Freeze protection is required with the application of steam coils. Possible system configurations are: face-and-bypass dampers and preheat/reheat coils. A freeze protection control scheme should include, shut down fan, close main steam valve, and dump condensate after the coils in case of power, steam, or instrument air failure. Filters Filter maintenance is often neglected. Many different filter designs have been used, including disposable filters, manual or automatic roll-up systems, and metal washable filters. Many systems are now designed with no filters, but with initial steam coils spaced at 5 fins per inch (fpi) or 5 mm. In these cases, coils are typically cleaned once or twice per year, depending on conditions. It may also be necessary to clean downstream components more frequently. Where filters must be used because of dust, insects, or sheet contamination problems, an effective filter maintenance program is required. Miscellaneous air systems It is recommended that inside air be used for roof heating, dryer section hood supply, motor cooling, and trim conveying systems. Roof heating and pocket ventilation systems typically draw air from the drive side mezzanine and serve as localized exhaust from these areas. They also help promote dry-end-to-wet-end and tending-side-to-drive-side air flows. Roof supply system Roof supply systems are designed to provide heated air to the truss area to prevent condensation of water vapor along the underside of the roof and on building steel. Machine rooms with a well insulated roof and effective former and wet end exhaust systems do not need a roof supply system. Most North American machine rooms have one form of roof supply system to protect the roof and structure during upset conditions. The roof and the wall above the crane rail should have sufficient insulation such that the surface temperature on the warm side of the vapor retarder is a minimum of 5°F or 3°C above the vapor dew point temperature. A design condition of 90°F or 32°C at 80% RH is typically used as a design point, but may vary according to climatic conditions. A minimum thermal resistance (R-value) of 18.0 ft2-°F-h/Btu or 3.2 K-m2/W, excluding air films, is recommended for cold climates. A vapor retarder located on the inside surface is required to prevent migration of vapor and air flow into the insulation. The vapor retarder location and installation is critical to the roofing system. Wet end systems are sized on flow per roof area basis, 1.5 cfm/ft2 (0.5 m3/min/m2), with a supply temperature of 120°F, 49°C, for a well ventilated machine and well insulated roof. Higher rates are needed for a building with a poorly insulated roof, ineffective exhaust systems to contain water vapor, or low make-up air balance. Wet end roof supply systems typically extend from two bays before the headbox to two bays past the press or press overhang. Dry end roof supply systems are installed in buildings with higher vapor loads, such as size press, open draws between sections, and coater areas. Most of these systems have steam coils, while some circulate unheated mezzanine air. One-sided distribution headers are common in newer machine rooms. The header is located along the drive side and discharges the air towards the tending side above the false ceiling. In buildings without a false ceiling, the header is located along the tending side, discharging the air towards the drive side roof exhaust fan inlets, creating a push-pull ventilation system.


Pocket ventilation, hood, and blow box supply Refer to TIP 0404-24 “Recommended operation of dryer section hood air systems” and TIP 0404-17 “Recommended minimum dryer pocket air requirements” for exhaust and pocket ventilation system description, guidelines for operation, and dimensioning. It is recommended that hood supply air systems use heated air drawn from the drive side mezzanine or truss level. Airflow requirements are based on process design for pocket ventilators and sheet stability devices. Typical recommended hood air mass balances are 55%–70% for a closed hood, and 30%–35% for an open hood. Motor cooling systems Motor cooling systems are no longer required except for special cases with the shift from DC to AC paper machine drive motors. AC motors use surface cooling provided by a fan mounted as part of the enclosure. DC motors rely on internal cooling supplied by a forced air cooling system. Motor suppliers specify cooling system airflow and static pressure requirements. Filtered, unheated basement air is generally used in this application to provide a relatively cool, but tempered, airflow and to provide air circulation in the basement. Care needs to be taken that the inlets are not near chemical exhausts that could damage motors. Airflow indicators and alarms are required for motor cooling systems to prevent drive motors from overheating. Two airflow indicators can be used—one in the main supply header to confirm system operation and one in the most remote drop duct to confirm integrity of the duct system. Air flow requirements range from 7 to-10 cfm/hp, 4.4 to 6.3 (m3/s)/MW, with an inlet pressure of 3 to 6 inches H2O, 750 to 1500 Pa, depending on the motor manufacturer and frame size. Trim systems Trim systems have a significant impact on ventilation around the pulpers and require air separation devices to reduce conveying air volume being introduced to the pulper enclosure. Conveying air flow rate is normally selected in the range of 1.5 to 2.0 lb of air per lb of trim with a conveying velocity equal to the maximum winder speed. Older systems were designed with higher air-to-trim ratios. Energy conservation and heat recovery The first step in conserving energy is to operate only the systems needed to meet the target temperature and humidity levels. Operating more exhaust fans than required for the current process conditions is wasteful and creates adverse conditions, particularly during the winter, such as fog and condensation, which adds to the heating load. The key is to minimize the amount of water vapor migrating into the building by:

Keeping dryer section hood doors closed at both operating and ground floor levels. Managing hood air systems to prevent hood from spilling heat and water vapor. Adding exhaust systems and shields to capture water vapor as close as possible to the source. Minimizing forming and press section shower water flow rates. Supplying only enough flow to the steam showers that can be condensed on the sheet or felt (lazy steam

showers). The next step in reducing energy is to utilize recovered energy to heat process water and ventilation air.


Heat recovery The dryer section is the single largest user of thermal energy within the mill. The majority of the energy exits through the hood exhaust to atmosphere. As much as 60 to 70% of this energy can be recovered. The extent of heat recovery is based on economic merits of energy savings versus installed cost. Heat recovery equipment is optimally sized to match heating requirements based on project economic criteria. The heat recovery system economic justification is a balance of recovery rate, operating and maintenance costs, and equipment cost. Factors to consider in selecting and sizing a heat recovery system:

Recovery rate o Heating requirements – seasonal loads may provide a higher rate of return than process loads in

cold climates. o Heat sources – What heat sources are available that reduce the system costs? o Incremental energy costs to meet peak requirements may be higher than the average. o Heat recovered may not meet total peak loads requiring supplemental heating. o Steam plant capacity – can the boiler capacity be reduced with heat recovery on new installations?

Operating and maintenance costs o Circulating fluid flow rate – lower flow rates with periodic higher pressure drops during peak

conditions may consume less energy on an annual basis. o Cost of maintaining the system – filters, steam traps, pumps, glycol systems, heat exchangers, and

showers. Equipment costs

o Heat recovery equipment – heat exchanger size is reduced by returning lower water temperature and increasing entering exhaust air humidity.

o Air make-up unit coils – fewer rows of coils are required with higher supply water glycol temperatures.

o Piping costs – decreasing circulation flow rate reduces pipes sizes. Heat sources For maximum heat recovery, hood exhaust humidity should be controlled at the design set point for the type of hood. Other sources of heat recovery are: boiler flue gas, vent steam from TMP and PGW processes, condensate not returned to the boiler (purchased steam), vacuum system water, and mill warm water system. Heating requirements Hood supply systems Pocket ventilation and hood supply systems have the highest temperature requirement of the heating loads. Non-condensing air-to-air heat exchangers can preheat the multi-cylinder hood supply from 80°F (27°C) to 120 to 140°F (49-to-60°C). Fresh or process water Process water can be heated directly or indirectly through a heat exchanger by the hood exhaust. Direct contact heat exchangers, or scrubbers, cost considerably less than indirect heat exchangers but will be contaminated with fiber. Building make-up systems Recovered energy can heat building make-up air either through an air-to-air exchanger or by circulating a water-glycol solution through an air-to-water exchanger to coils mounted in the building make-up air units.


The minimum glycol concentration is 25% by volume to ensure adequate corrosion inhibitor is present. The required concentration should prevent the system from freezing at the lowest expected ambient condition in case of power failure. Three basic types of heat exchangers are used to recover heat from the exhaust stream:

Air-to-air Indirect air-to-water Direct air-to-water

Air system surveys and performance indices The following questions should be asked when evaluating existing building air systems:

1. Are there signs of corrosion on the building structure? 2. Is there any condensation along the underside of the roof or upper walls? 3. Is the water vapor contained and exhausted in the forming and press sections? 4. Is there fog or condensation during cold weather? 5. Are the dryer section hoods spilling? 6. Is the building under a high negative pressure? Do the personnel doors slam closed or are they hard to

open? 7. Are there cold spots in the building during winter months? Conversely, are there hot spots during summer

months? 8. What are the temperatures and humidity levels and how do they compare to the recommended levels listed

on page 3 of this TIP? 9. How does current energy consumption compare to previous years?

10. What equipment, by simple investigation, is obviously not performing as designed? Why not? In the event that more detailed (and costly) investigation is warranted or desired, a detailed air system survey can be performed which should include the following:

Investigation of operator and maintenance issues with the air systems Identification of areas of heat and vapor spill Inspection of mechanical condition of fans, coils, filters, dampers, ductwork, hoods, etc. Measurement of fan air flows, temperatures, humidities, static pressures, rpm, and motor loads Measurement of infiltrating and exfiltrating air flows Spot temperature and humidity readings throughout the building to establish airflow requirements Calculation of performance indices Recommendations to improve performance

Table 2 is an outline of information required for evaluation of the measured performance and comparison to the recommended flows and performance indices. Performance indices Overall performance

Total exhaust air per pound of paper produced – Total building exhaust (scfm or m3/min) divided by production rate (lb/minute or kg/minute):


Grade Target Exhaust Rate: Winter – Summer lbDA/lb paper (kgDA/kg paper) ft3/lb paper m3/kg paper

Bleached Board 40.9 – 48.4 545 – 645 36.4 – 43.1 Corrugating Medium 28.1 – 40.9 375 – 545 25.0 – 36.4 Fine Paper 39.8 – 47.3 530 – 630 35.4 – 42.1 Linerboard 28.1 – 43.1 375 – 575 25.0 – 39.4

In the past, air change rates were the main criteria for designing machine room ventilation systems. However, air change alone is an inadequate measure of the air volume required. Air change does not take into account process exhaust requirements or air distribution. Small machine rooms, buildings with multiple machines, machines with open dryer hoods, and machines with high production rates can have high air change rates, but still have inefficient ventilation systems.

Building air balance – Machine room air balance is the amount of air supplied to the room divided by the amount of exhaust air.

Maintenance performance o Percent of exhaust fans and air make-up units that are operational o Percent of filters on heating coils that are clean

System specific

Dryer section hood and associated systems – Performance indicators for conventional dryer section hoods (excluding Yankees or through-air dryers) include the following:

Index

Units Open Hood Closed Hood

High Performance Closed Hood

Hood Exhaust Humidity grains H2O/lbDA kg/kg

400 0.06

800 0.14

1100 0.16

Hood Air Balance % 35 70 60

Wet end air change rate – Building volume above the operating floor (floor to underside of false ceiling),

from the headbox through the wet end of the dryer hood divided by total standard volume flow rate of forming section and wet end false ceiling exhaust. This indicator can be used to check forming section and wet end false ceiling exhaust volumes. Machine speed and stock temperature greatly affect wet end exhaust requirements; therefore, this index should be used with caution.

Supply system performance – Analyze make-up air supply flow rates and compare actual to recommended

values. o Air distribution o Wet end air balance o Supply operating floor air change rate o Basement air change rate

Energy performance

Supply air temperature – systems operating with higher than required supply temperatures. Systems introducing outside air – systems not utilizing heat from within the building. Summer versus winter operation – operating more exhaust fans for than required. Operating cost – high energy consumption per ton of paper produced. Heat recovery utilization – Opportunities to reduce operating cost.

Special cases Most performance indicators and design parameters discussed are based on a single paper machine housed in its own building. The air system must be modified for other machine configurations.


Two machines in a common building A complication in ventilation system design occurs when the machine room houses two machines with a common tending aisle. It is extremely difficult to get sufficient airflow to the tending aisle in this case. Open hoods make it even more difficult to achieve desired airflows. All possible efforts should be made to get supply air ducted to the tending aisle, especially at the forming section. A number of creative approaches have been used to improve airflows in this situation. Possibilities include:

Concentrate as much supply air as practical at the wet end and dry end of the machines. Provide air from drive side air make-up units (AMUs) through concrete trenches beneath the

machines. Provide air through insulated ducts run across the dryer section hoods (crane, hood door, and aisle

clearance can make this very difficult). Use ducted or skirted man coolers to provide the coolest air as possible from the basement floor level. Furnish equipment platforms or mezzanines between the machines for AMUs with roof level intake.

Multiple machines in a common building The problem of two machines in a common building can be compounded with additional machines. Areas where two machines are back-to-back are especially difficult to ventilate. Possibilities to improve ventilation in these common drive aisles include:

Gratings in the mezzanine floor and increased roof exhaust over the drive aisle can help. Minimize heat and vapor spill from the drive side of the paper machines. Good hood closure is a key. Provide supply air from the roof or any available area. Increase summer building exhaust rate.

Enclosed mezzanine Enclosing the mezzanine and leaving it open opposite the forming and press sections can reduce the exhaust requirements by using the pocket ventilation system as part of the exhaust system. The mezzanine is enclosed by walls at the dry end and along the length of the machine. Instead of short-circuiting the air from the dry end room supply air units to the pocket ventilation units, air is forced to the wet end of the machine room where it is more effective in capturing vapor. Dry-end-to-wet-end velocity is increased, which prevents vapor from spilling towards the dry end from the forming and press sections. Because of increased airflow across the wet end of the machine, the amount of wet end false ceiling exhaust can be decreased while maintaining a good ventilation effect. An enclosed mezzanine is not recommended for operations with stock temperatures greater than 120°F (49°C), high paper dust concentration, or buildings with structural steel exposed at the wet end. Tissue machine room ventilation Tissue machine rooms provide additional ventilation challenges because of dry end dusting, heat from the Yankee air systems, and hot burner rooms for the Yankee air system. A well-balanced Yankee hood and an effective primary dust-control system are the best ways to control problems at their source and avoid problems with machine room ventilation. Other ventilation approaches can be used to balance each area of the machine and prevent dust from migrating towards the wet end of the building. Strong tending-side-to-drive side airflows are still recommended, but building exhaust should be distributed throughout the length of the building to balance the tending aisle supply.


Air system operation Air systems should be designed to operate with little operator attention. Operators should be notified automatically when the systems are not operating properly and require maintenance. Instructions and labels should be provided at the operator control panel or on the DCS computer control screen clearly stating which fans should operate at all times and which ones are for summer only. Modern dryer ventilation control systems adjust supply and exhaust flow rates based on measured drying rates on the machine. This approach ensures good ventilation without wasting energy. These systems require a reliable and accurate measurement of the drying rates for effective control. Air system maintenance Periodic maintenance of ventilation system components is important for effective long-term operation. Autumn checkout, start-up, and “winterizing” of ventilation systems are also important steps to ensure effective system operation. Heating coil systems should be brought on line as necessary. Systems require checking and maintenance every three to six months.

Air filters require special attention and should be attended to at intervals determined by local dust loading conditions. Keywords Ventilation, Machine rooms, Materials balance, Heat, Water vapor, Dust, Exhaust gas, Air, Infiltration, Filters, Motors, Trim, Energy conservation, Heat recovery, Performance Additional Information

Effective date of issue: April 29, 2015 Working Group:

Jeff Reese, Chair, International Paper, Chairman John Nielsen, KBR Laurie Coulson, LLC2 Pekka Kormano, Deublin Steam Systems Ray Krumenacker, Consultant Dick Reese, Dick Reese and Associates Greg Wedel, Kadant Literature cited 1. U.S. Department of Health and Human Services, Occupational Exposure to Hot Environments Revised

Criteria, National Institute for Occupational Safety and Health (NIOSH), 1986. 2. U.S. Department of Labor, Occupational Safety & Health Administration Standard 29 CFR 1910.1000, Air

Contaminants. http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9991 (retrieved December 2008).

3. Goodfellow, H. D. and Tahti, E. (Eds.), Industrial Ventilation Design Guidebook, Academic Press, 2001. 4. Zhivov, A. M., Nielsen, P. V., Riskowski, G., Shilkrot, E., “Displacement Ventilation for Industrial

Applications Types, Applications and Design Strategy”, Heating/Piping/Air-Conditioning, March 2000. 5. TAPPI, TIP 0502-01, “Paper machine vacuum selection factors”, TAPPI, Atlanta, Georgia, 2007. 6. TAPPI, TIP 0404-27, “Press fabric dewatering and conditionings-suction box (Uhle box), and vacuum

requirements” TAPPI, Atlanta, Georgia, 2007. 7. TAPPI, TIP 0404-24, “Recommended operation of dryer section hood and air systems”, TAPPI, Atlanta,

Georgia, 2001.


8. TAPPI, TIP 0404-17, “Recommended minimum dryer pocket air requirements”, TAPPI, Atlanta, Georgia, 2005.

9. The Dow Chemical Co., Engineering and Operating Guide for Dowtherm SR-1 and Dowtherm 4000 Inhibited Ethylene Glycol-based Heat Transfer Fluids, February 2008.

10. The Dow Chemical Co., Engineering and Operating Guide for Dowfrost and Dowfrost HD Inhibited Propylene Glycol-based Heat Transfer Fluids, September 2001.

References Hines, A., Mass Transfer: Fundamentals and Applications, Prentice-Hall, 1984. Schmidt, K., “Saving Process Energy in the Papermaking Industry”, Paper, 7, December 1981. Sundqvist, H., “Dryer Section Ventilation and Heat Recovery” in Papermaking Science and Technology: Papermaking Part 2, Drying (M. Karlsson, Ed.), Fapet Oy, 2000. Table 1. English to metric conversions

Property To convert values expressed in

CUSTOMARY UNITS

Multiply by To obtain values expressed in

RECOMMENDED FORM

Name [Symbol] *exactly Name [Symbol]

Air flow cubic feet per minute [cfm] 1.69901 cubic meters per hour [m3/hr]

Air flow per width cubic feet per minute per inch width

[cfm/in.]

66.89 cubic meters per hour per meter [m2/hr]

Air flow per area cubic feet per minute per square foot

[cfm/ft2]

18.2875 cubic meters per hour per square meter

[m3/hr/m2]

Area square feet [ft2] 0.0929030 square meters [m2]

Coil spacing fins per inch [fpi] *fs=(1/fpi) x25.4 fin space (millimeters) [mm]

Humidity lb water vapor per lb dry air [lb water/lb

d.a.]

grains/lb dry air [grains]

*1

*1/7000

kilogram water per kilogram dry air [kg

water/kg d.a.]

kilogram water per kilogram dry air [kg

water/kg d.a.]

Length feet [ft]

inches [in.]

*0.3048

*25.4

meters [m]

millimeters [mm]

Mass pounds [lb] 0.453592 kilograms [kg]

Mass flow pounds dry air per minute [lb da/min] 0.453592 kilograms dry air per minute [kg da/min]

Power horsepower [hp] 0.74570 kilowatts [kW]

Production rate short tons per day [tpd] 0.907185 metric tons per day [tpd]

Temperature degrees Fahrenheit [F] TC=(TF-32)/1.8 degrees Celsius [C]

Temperature interval degrees Fahrenheit change [F] 0.555556 degrees Celsius change [C]

Specific volume cubic feet per pound dry air [ft3/lb d.a.] 0.062428 cubic meters per kilogram dry air [m3/kg

d.a.]

Velocity feet per minute [fpm]

feet per minute [fpm]

5.08

*0.3048

millimeters per second [mm/s]

meters per minute [m/min.]

Volume cubic feet [ft3] 0.0283169 Cubic meters [m3]


Appendix A. Sample calculation 1 Parameters

Grade: Linerboard Production rate: 1 899 TPD (79.12 TPH) at 100% efficiency Reel trim: 274 inches Design speed: 3000 ft/min Former: Fourdinier with top wire former Silo configuration: Base sheet: on-machine Stock temperature: 140°F Steam boxes: Fourdrinier and press Dryer section: Moisture - Press / Reel: 52% / 7%

High performance hood, exhaust humidity: 0.1600 lbH2O/lbDA Infiltration humidity: 0.0214 lbH2O/lbDA

Former exhaust

Fourdrinier

3274 3000 ft

12000 12000 1.8 110 40016.67 16.67 min

vt

V Cw

Compared flow rate to the machine direction face velocity: Machine-direction face velocity: Breast roll to wire turning roll distance = 101 ft Operating floor to wire = 12 ft Face area = 2101 ft 12 ft 1 212 ft

Minimum exhaust = 3ft ft

100 101 ft 12 ft 121 200min min

Since V

= 110 400 ft3/min is less than the minimum exhaust, 121 200 ft3/min. Increase V

by 10 800 ft3/min.

Top Wire

3274 3000v ft6000 6000 1.8 72 500

24 24 mint

wV C

Recommended top wire former exhaust is 72 500 ft3/min. Total recommended former exhaust is 193700 ft3/min.

Vacuum pump/blower exhaust

3scfm ft

274in 150 41100in min

V


Production – dry basis 100 ton lb day lbBDpaper

1 899 2000 1 0.07 147 173100 day ton 24 hr hr

exitdry MD

MP P

Evaporation ratio 20.52 0.07 lbH O1.01

1 1 1 0.52 1 0.07 lbBDpaperin out

ratioin out

M ME

M M

Evaporation rate 2

2 2lbH O lbBDpaper lbH O1.01 147 173 148644

lbBDpaper hr hrH O ratiom E P

Exhaust mass 2 2

2

lbH O 1 lbDA lbDA148 644 1 072 468

hr 0.16 0.0214 lbH O hrH O

exh

mm

w

or

lbDA17874

min

19 / Paper machine room ventilation guidelines TIP 0404-50

Pulper exhaust

Press pit: 3 3ft 274 in ft

720 16 440inmin-ft min12ft

Reel pulper: 3 3ft 274 in ft


Saveall exhaust

Base sheet and top ply savealls: 3 3ft ft

2 2 500 5 000min min

Building exhaust – Wet end false ceiling

Distance from headbox to dryer section = 160 ft

3

v 10

100

3000 10 274 in 274 in ft160ft 1.87 1.25 2 2000 1.0 432 900

in in100 1 min12 12ft ft

t w

Area

V AC C nDw EC

Supplemental roof exhaust

Production rate: 79.12 tons per hour. Refiners located on operating floor and vacuum pumps in a separate room. Ground floor heat load: Btu/ton Stock preparation pumps and piping: 20 000 Former & press pumps and piping: 75 000 Subtotal – ground floor: 95 000 Ground floor heat load = (95 000 Btu/ton)(79.12 ton/hr) = 7.52 x106 Btu/hr Operating floor heat load: Refiners: 51 700 PM Drive - forming & press 51 600 - dryer 18 500 - calender 14 500 - reel 8 600 - winder 44 400 Subtotal – operating floor: 189 300 Operating floor heat load = (189 300 Btu/ton)(79.12 ton/hr) = 14.98 x106 Btu/hr

Minimum exhaust rate =

63

Btu 1 hr7.52 14.98 10

fthr 60 min13.33 833 125scfm

Btu lbDA0.24 25 Flbm- F

gp

Qv

c t


Process exhaust: scfm Remarks Saveall 4 200 Convert to scfm = (5 000 acfm)(13.33/15.8) Vacuum pumps 41 100

Former 168 800 Convert to scfm = (193 700 acfm)(13.33/15.3) Wet end false ceiling 387 300 Convert to scfm = (432 900 acfm)(13.33/14.9) Dryer hood 238 300 Convert to scfm = (17 874 lbDA/min)(13.33 ft3/lbDA)

Pulpers 29 800 Convert to scfm = (32 900 acfm)(13.33/14.7) Total Process Exhaust 869 500 The total process exhaust rate including wet end false ceiling exhaust exceeds recommended rate. However, with all the exhaust being drawn from below the false ceiling additional exhaust is recommended from the truss space: Wet end truss 96 800 25% of 387 300 scfm (w/ false ceiling) Dry end 23 800 10% of 238 300 scfm (w/ false ceiling) Supplemental 120 600 or 132 400 acfm

Add 3-45 000 cfm (123,000 scfm) fans exhausting from truss area, two at the wet end and one at the dry end. Total winter exhaust = 869 500 + 123 000 = 992 500 scfm

Summer roof exhaust


3

6 6

ft13.33

lbDA 7.52 10 Btu 14.98 10 Btu1 250 800scfm

min Btu 10 F hr 25 F hr60 0.24hr lbm- F

gp

Qv

c t

Increase summer exhaust rate by 258 300 scfm or 6 - 45 000 cfm roof exhaust fans to meet warm weather operation. Locate two fans in the stock preparation, two over the mezzanine, and two at the dry end. All fans should be located over the drive aisle.

Supply System

Make-up air Use a winter balance of 100%: 100% 992 500 scfm 992500 scfmsupply exhaustm R m

Summer Balance 992500scfm

0.791 250 800 scfm

Make-up air distribution, scfm Floor Level Total Tending Side Drive Side Mezzanine 49 600 (0.05) - 49 600 (0.05) Operating 694 800 (0.70) 545 900 (0.55) 148 900 (0.15) Ground 248 100 (0.25) 148 900 (0.15) 99 200 (0.10) Total 992 500 (1.00) 694 800 (0.70) 297 700 (0.30)

Roof supply

Wet end roof supply Wet end coverage, two bays before former and two bays past press = 160 ft + 4(20 ft) = 240 ft Distance between crane columns = 84 ft

3 3

2

ft ft1.5 240ft 84ft 30 240

min ft minV


Performance Indices

EXHAUST Units

Winter exhaust per lb of paper ft3/lb 992 500 scfm

376ton lb 1 hr

79.12 2000hr ton 60 min

lbDA/lb 3

3

ft 1 lbDA376 28.2

lb paper 13.33 ft

Summer exhaust per lb of paper ft3/lb 1 250 800 scfm

474ton lb 1 hr

79.12 2000hr ton 60 min

lbDA/lb 3

3

ft 1 lbDA474 35.6

lbpaper 13.33 ft

Winter air change rate minute

3

112ft 824ft 75ft7.0

ft992 500

min

Building volume

Exhaust Rate

Summer air change rate minute

3

112ft 824ft 75ft5.5

ft1 250 800

min

Building volume

Exhaust Rate

Wet end air change rate minute

3

84ft 160ft 51ft1.23

ft168 800 387 300

min

Wet end volume

Exhaust Rate

Former exhaust scfm/in

trim

3ft193 700

min 707274 in

Wet end false ceiling exhaust scfm/ft2

3ft387 300

min 106274

ft 160ft12

False Exhaust Rate

Area

SUPPLY Winter air balance % 100

Summer air balance % 79 Distribution – Ground Floor % 25

Operating Floor % 70 Tending % 55

Drive % 15 Mezzanine % 5

Operating floor supply air change min

3

112ft 824ft 10ftOperating floor volume1.3

ftOperating floor supply rate694 800

min

Ground floor supply air change rate min

3

112ft 824ft 24ftGround floor volume8.9

ftGround floor supply rate248 100

min


Appendix B. Sample calculation 2 Parameters

Grade: Copy grade Production rate: 1516 TPD (63.2 TPH) at 100% efficiency Reel trim: 365 inches Design speed: 4500 ft/min Former: Gap former Silo configuration: Off-machine Stock temperature: 120°F Steam boxes: None Dryer section: Press moisture/Main exit moisture: 60% / 2%

After moisture/Reel moisture: 28.8% / 5% Size application: 100 lb/MDton High performance hood Main hood exhaust humidity: 0.1600 lbH2O/lbDA After hood exhaust humidity: 0.1290 lbH2O/lbDA Infiltration humidity: 0.0214 lbH2O/lbDA

Former exhaust

Gap Former

3ft ft ft

0.11v 0.11 4500 365 in 1.0 180 700in min mintV wC

Vacuum pump/blower exhaust

3scfm ft

365in 150 54 750in min

V


Reel

Production – dry basis Reel 100 ton lb day lbBDpaper

1516 2000 1 0.05 120 017100 day ton 24 hr hr

exitdry MD

MP P

Main

Size added lb ton lb

100 63.2 6 317ton hr hrsize size MDm A P

Production – Base sheet Main Reel lbBDpaper120 017 6 317 113 700

hrdry dry sizeP P m

Evaporation ratio Main 20.60 0.02 lbH O1.48


ratioin out

M ME

M M

Evaporation rate 2

Main Main Main 2 2lbH O lbBDpaper lbH O1.48 113 700 168 230

lbBDpaper hr hrH O ratio drym E P

Exhaust mass – Main 2

MainMain 2

Main 2

lbH O 1 lbDA lbDA168 230 1 214 028

hr 0.16 0.0214 lbH O hrH O

exh

mm

w

or

lbDA20 234

min

After

Evaporation ratio After 20.288 0.05 lbH O0.353


ratioin out

M ME

M M

Evaporation rate 2

After After Reel 2 2lbH O lbBDpaper lbH O0.353 120 017 42 326

lbBDpaper hr hrH O ratio drym E P

Exhaust mass – After 2

AfterAfter 2

After 2

lbH O 1 lbDA lbDA42 326 393 364

hr 0.129 0.0214 lbH O hrH O

exh

mm

w

or

lbDA6 556

min


Pulper exhaust

Press pit: 3 3ft 365 in ft


Size press pulper: 3 3ft 365 in ft


Reel pulper: 3 3ft 365 in ft


Winder pulper: 3 3ft 365 in ft


Saveall exhaust

Saveall: 3ft

2 500min

Building exhaust – Wet end false ceiling

Distance from No. 1 outer loop to dryer section = 103.8 ft

3

v 10

100

4500 10 365in 365in ft103.8ft 1.0 1.25 0 2000 1.0 217 100

in in100 1 min12 12ft ft

t w

Area

V AC C nDw EC

Size press and coater false ceiling exhaust

Distance between main and after dryer section hoods = 25 ft

3ft 365in ft

0.0242v 0.0242 4 500 14.8 25ft 94 100inmin min12ft

V B A

Supplemental roof exhaust

Production rate: 63.2 tons per hour. Refiners located in a separate area and vacuum pumps are located outside. Ground floor heat load: Btu/ton Stock preparation pumps and piping: 20 000 Former & press pumps and piping: 75 000 Subtotal – ground floor: 95 000 Ground floor heat load = (95 000 Btu/ton)(63.2 ton/hr) = 6.00 x 106 Btu/hr


Operating floor heat load: Refiners: 0 PM Drive - forming & press 51 600 - main dryers 18 500 - size press 3 200 - after size dryers 6 400 - calender 14 500 - reel 8 600

- winder 44 400 Subtotal – operating floor: 147 200 Operating floor heat load = (147 200 Btu/ton)(63.2 ton/hr) = 9.30 x 106 Btu/hr Cleaners = (1 000 Btu/h/ft2)(1 275 ft2) = 1.28 x 106 Btu/hr


63

Btu 1 hr6.00 9.30 1.28 10

fthr 60 min13.33 613 900scfm

Btu lbDA0.24 25 Flbm- F

gp

Qv

c t

Process exhaust: scfm Remarks Saveall 2 200 Convert to scfm = (2 500 acfm)(13.33/15.2)

Vacuum pumps 54 800 Former 162 800 Convert to scfm = (180 700 acfm)(13.33/14.8) Wet end false ceiling 203 800 Convert to scfm = (217 100 acfm)(13.33/14.2) Main dryer hood 269 700 Convert to scfm = (20 234 lbDA/min)(13.33 ft3/lbDA) After dryer hood 87 800 Convert to scfm = (6 584 lbDA/min)(13.33 ft3/lbDA)

Size press false ceiling 82 500 Convert to scfm = (94 100 acfm)(13.33/15.2) Pulpers 71 500 Convert to scfm = (78 500 acfm)(13.33/14.8) Total Process Exhaust 935 100 The total process exhaust rate including wet end false ceiling exhaust exceeds the recommended rate. However, with all the exhaust being drawn from below the false ceiling additional exhaust is recommended from the truss space: Wet end truss 50 900 25% of 203 800 cfm (w/ false ceiling) Dry end 35 800 10% of 357 500 scfm (w/ false ceiling) Supplemental 86 700 or 95 100 acfm

Add 2-48 000 cfm (87,500 scfm) fans exhausting from the truss area, one at the wet end and one at the dry end. Total winter exhaust = 935 100 + 87 500 = 1 022 600 scfm

Summer roof exhaust


3

66

ft13.33

9.30 1.28 10lbDA 6.00 10 Btu Btu947 200 scfm

min Btu 10 F hr 25 F hr60 0.24hr lbm- F

gp

Qv

c t

Winter exhaust rate exceeds recommended minimum summer exhaust rate. No additional roof exhaust fans are required.

Supply System

Make-up air Use a winter balance of 105%: 105% 1 022 600 scfm 1 073 700 scfmsupply exhaustm R m

Summer Balance 1 073 700 scfm

1.051 022 600 scfm

Make-up air distribution, scfm Floor Level Total Tending Side Drive Side Mezzanine 53 700 (0.05) - 53 700 (0.05) Operating 740 600 (0.70) 590 500 (0.55) 161 100 (0.15) Ground 268 400 (0.25) 161 100 (0.15) 107 300 (0.10) Total 1 073 700 (1.00) 751 600 (0.70) 322 100 (0.30)


Roof supply

Wet end roof supply Wet end coverage, two bays before former and two bays past press = 160 ft + 4(20 ft) = 240 ft Distance between crane columns = 84 ft

3 3

2

ft ft1.5 240ft 84ft 30 240

min ft minV

Performance Indices

EXHAUST Units

Winter exhaust per lb of paper ft3/lb 1 022 600 scfm

485ton lb 1 hr

63.2 2000hr ton 60 min

lbDA/lb 3

3

ft 1 lbDA485 36.4

lbpaper 13.33 ft

Summer exhaust per lb of paper ft3/lb 485 lbDA/lb 36.4

Winter air change rate minute

3

132ft 827ft 78ft8.3

ft1 022 600

min

Building volume

Exhaust Rate

Summer air change rate minute 8.3

Wet end air change rate minute

3

104ft 104ft 53ft1.56

ft162 800 203 800

min

Wet end volume

Exhaust Rate

Former exhaust scfm/in

trim

3ft162 800

min 446365 in

Wet end false ceiling exhaust scfm/ft2

3ft203 800

min 64.4365

ft 104ft12

False Exhaust Rate

Area

SUPPLY Winter air balance % 105

Summer air balance % 105 Distribution – Ground Floor % 25

Operating Floor % 70 Tending % 55

Drive % 15 Mezzanine % 5

Operating floor supply air change min

3

132ft 827ft 10ftOperating floor volume1.47

ftOperating floor supply rate740 600

min

Ground floor supply air change rate min

3

132ft 827ft 25ftGround floor volume10.2

ftGround floor supply rate268 400

min

TIP 0404-50 Paper machine room ventilation guidelines

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Transcript of TIP 0404-50 Paper machine room ventilation guidelines