Date: November 16, 2011

Subject: Section 112(d)(6) Technology Review for Pulping and Papermaking 

Processes

EPA Contract No. EP-D-11-084; Work Assignment No. 0-03

From: Katie Hanks

Thomas Holloway

To: John Bradfield

Bill Schrock

U.S. Environmental Protection Agency

Research Triangle Park, NC 27711

The purpose of this memorandum is to present the results of a review of available 

information on developments in practices, processes, and control technologies that apply to 

pulping and papermaking processes. This analysis is part of the U.S. Environmental Protection 

Agency’s (EPA’s) effort to review the national emission standards for hazardous air pollutants 

(NESHAP) for the Pulp and Paper Industry (40 CFR part 63, subpart S) in accordance with 

section 112(d)(6) of the Clean Air Act (CAA).

Section I of this memorandum provides background information on the requirements of 

section 112(d)(6) of the CAA, the pulp and paper production source category, and the 

requirements of the Pulp and Paper NESHAP. Section II discusses the review of information on 

developments in practices, processes, and control technologies that have occurred since the 

original development of this NESHAP. The specific processes mentioned in this memorandum 

include:

 Kraft pulping processes

 Soda pulping processes

 Semichemical pulping processes

 Sulfite pulping processes

 Non-wood pulping processes

 Mechanical pulping

 Secondary fiber pulping processes

 Papermaking processes

Separate memoranda present detailed technology reviews for kraft pulping process condensates 

and bleaching systems. (EPA 2011a, EPA 2011b)
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I. Background

A. Requirements of Section 112(d)(6) of the CAA

Section 112 of the CAA requires EPA to establish technology-based standards for 

sources of hazardous air pollutants (HAP). These technology-based standards are often referred 

to as maximum achievable control technology (MACT) standards. Section 112 also contains 

provisions requiring EPA to revisit these standards. Specifically, paragraph 112(d)(6) section 

states:

(6) REVIEW AND REVISION. – The Administrator shall review, and revise as 

necessary (taking into account developments in practices, processes, and control 

technologies), emission standards promulgated under this section no less often

than every 8 years.

For the purpose of this technology review, a “development” was considered to be any of 

the following:

 Add-on control technology or other equipment that was not identified and considered 

during the development of the NESHAP;

 Improvements in add-on control technology or other equipment that were not identified 

and considered during NESHAP development that could result in significant additional 

HAP emissions reductions;

 Work practice or operational procedure that was not identified and considered during 

NESHAP development; and

 Process change or pollution prevention alternative that could be broadly applied that was 

not identified and considered during the development of the NESHAP.

 Improvements in work practices, operational procedures, process changes or pollution 

prevention alternatives

B. Description of Source Category and NESHAP Requirements

The pulp and paper production source category includes any facility engaged in the 

production of pulp and/or paper. This category includes, but is not limited to, integrated mills 

(where pulp alone, or pulp and paper, or paperboard are manufactured on-site), non-integrated 

mills (where either pulp or paper/paperboard are manufactured on-site, but not both), and 

secondary fiber mills (where waste paper is used as the primary raw material).

The processes used to convert wood into paper products include: wood preparation 

(debarking, chipping, and sizing of the wood material); pulping (chemical, mechanical, 

semichemical, or recycled paper pulping); chemical recovery (recovery of pulping chemicals in 

chemical and semichemical pulping); bleaching (chemically whitening/brightening the pulp);

and papermaking (stock preparation, dewatering, pressing, drying, and finishing). A fullyintegrated chemical pulp and paper mill would include all of these process areas.
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The MACT standards for the pulp and paper production source category were developed 

in three parts:

 MACT I - regulates HAP emissions from the pulp production areas and bleaching 

operations at chemical pulp mills (kraft, sulfite, semichemical, and soda wood pulping 

processes) and the bleaching operations at pulp mills using mechanical, secondary fiber, 

and non-wood pulping;

 MACT II - regulates HAP emissions from the chemical recovery combustion areas of 

chemical pulp mills (kraft, sulfite, semichemical, and soda wood pulping processes); and 

 MACT III - regulates HAP emissions from pulp and paper production areas of pulp mills 

using mechanical, secondary fiber, and non-wood pulping, and papermaking systems at 

all mills.

The MACT I and MACT III standards are contained in 40 CFR part 63, subpart S 

(NESHAP for the Pulp and Paper Industry), which was promulgated on April 15, 1998. As noted 

previously, the purpose of this memorandum is to present the results of a technology review for 

many sources subject to NESHAP subpart S.

The pulping and bleaching operations at kraft, soda, sulfite, and stand-alone 

semichemical pulp mills that are regulated by the MACT I rule include digesters, pulp washers, 

evaporators, turpentine recovery, steam stripper systems, liquor storage tanks, lime slaker vents, 

oxygen delignification systems, bleaching systems, wastewater treatment systems, and related 

equipment and processes. Bleaching operations at mechanical, secondary fiber, and non-wood 

pulp mills that are regulated by the MACT I rule include bleaching tower vents, storage tanks, 

washer vents, filtrate tank vents, scrubber outlets, and wastewater. Mills that mechanically pulp 

wood, pulp secondary fiber or non-wood fibers, and any mills that make paper, paperboard, or 

related products from pulp are entities covered by the MACT III rule. The processes evaluated 

under this standard include chip pre-steaming vessels, pulpers/repulpers, deinking operations at 

secondary fiber mills, and papermaking operations (e.g., forming, drying, vacuum pumps, 

storage tanks) at all mills.

As promulgated, the MACT I and III (subpart S) standards include emissions standards 

for pulping system vents, kraft pulping process condensates, and bleaching system vents. These 

standards also include several alternative emissions limits for each covered process that is

designed to provide flexibility and promote and encourage the use of new technology, 

particularly combined air/water controls and pollution prevention technologies. Table 1 at the 

end of this memorandum presents an abbreviated summary of the subpart S standards. The 

control systems used by most mills to meet the subpart S emissions standards are as follows:

 Pulping system vents — thermal oxidizers, power boilers, lime kilns, and recovery

furnaces.

 Pulping process condensates — steam strippers, biological wastewater treatment, and 

recycling to pulping equipment that is controlled by the standards.

 Bleaching system vents — caustic scrubbers (for chlorinated HAP other than chloroform) 

and process modifications to eliminate the use of chlorine and hypochlorite.
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C. Estimated HAP Emissions

Substantial HAP emission reductions have been achieved through implementation of 

subpart S for pulping and bleaching vents and kraft condensates. Nationwide baseline HAP 

emissions for the subpart S source category were estimated at 230,000 tons per year (tpy) prior to 

implementation of subpart S. (EPA1993) The EPA conducted an information collection request 

(ICR) in 2011 that requested updated emissions inventories from major source pulp and paper 

production facilities. Post-MACT nationwide emissions estimates based on responses to Part II 

of the pulp and paper ICR were 44,726 tpy. Methanol accounts for 86 percent of the total HAP 

emissions, while acetaldehyde accounts for 5 percent. Numerous other HAP account for the 

remaining emissions reported for subpart S equipment in Part II of the ICR. Table 2 at the end of 

this memorandum presents a list of the pollutants and their reported emissions for equipment in 

the subpart S source category. Figure 1 depicts the magnitude of subpart S emissions by process.

Processes with the most emissions following MACT implementation are kraft pulping, 

wastewater, and papermaking. Bleaching emissions remain as well, but are not of the same 

magnitude as the aforementioned processes. Emissions from non-kraft pulping processes are 

very low relative to kraft pulping, in part because there are fewer of these processes nationwide, 

and because the emissions sources in these processes differ from kraft processes. 

At the time of subpart S promulgation, it was concluded that wood yard operations, tall 

oil recovery systems, and pulping systems at mechanical, secondary fiber, and non-wood fiber 

pulping mills do not emit significant quantities of HAPs. (72 FR 18519, April 15, 1998) As 

clearly shown in Figure 1 for tall oil and mechanical pulping, this conclusion remains true today

following MACT implementation. Wood yards do not appear in Figure 1 because no HAP data 

for wood yards were reported in the Part II subpart S inventory. Secondary fiber operations also 

are not shown separately on Figure 1 because they are often co-located with and integrated into 

other pulping or papermaking operations, and, therefore, secondary fiber emissions are 

embedded in the Figure 1 bars for other processes. There are no known major source non-wood 

mills (e.g., the only non-wood mill responding to the ICR was found to be a true area source).

Consequently, the remainder of this memorandum focuses on chemical pulping processes and 

papermaking with limited additional discussion of the processes noted in this paragraph.

II. Developments in Practices, Processes, and Control Technologies 

The RACT/BACT/LAER Clearinghouse (RBLC) and responses to Part I of EPA’s pulp 

and paper ICR were reviewed to determine if there have been developments in practices, 

processes, or control technologies for pulping and papermaking. In addition, we contacted states 

for details on BACT determinations made for papermaking processes. No new measures for 

reducing pulping HAP emissions were identified beyond the technologies used to comply with 

MACT for most equipment. A separate memorandum discusses the technology review for kraft 

condensates (wastewater), where a separate investigation was performed. The technology review 

for bleaching is also provided in a separate memorandum, though no new emissions reduction 

measures were identified.
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A. RACT/BACT/LAER Clearinghouse

The information found in our search of the RBLC is described and tabulated in a separate 

memorandum. (RTI 2011a) A few emissions reduction measures for pulping processes were 

identified in the RBLC. Pulping emissions of HAP, volatile organic compound (VOC), total 

reduced sulfur (TRS), and/or acetone at 12 kraft pulp mills were controlled by routing them to an 

incineration device, such as a boiler, lime kiln, recovery furnace, or thermal oxidizer. Pulping 

condensate VOC and TRS emissions in wastewater at two mills were controlled by

biodegradation or good management practices. In each of these cases, the information obtained

through the RBLC search did not represent any practices, processes, or control technologies not 

already identified and evaluated during the original MACT development. The findings of EPA’s 

ICR relative to these controls are described below.

Controls other than those considered as HAP-reducing technologies during the original 

MACT development were also noted in the RBLC for some processes. Specifically, lime slaker 

particulate matter (PM) emissions at one mill were controlled by a wet scrubber. Tall oil 

recovery system VOC emissions at one mill were controlled by venting them to incinerationbased control. Pulping VOC emissions were controlled at two mechanical pulp mills by using a

regenerative thermal oxidizer (RTO) and at one mill by using existing fiber 

scrubbers/condensers. Non-HAP VOC (e.g., pinenes) are the predominant pollutants from tall oil 

recovery and mechanical pulping systems. TRS may also be important for tall oil recovery.
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B. Review of Pulp and Paper Part I Survey Data

1. Kraft pulping processes

Ninety-seven mills in the Part I data base perform kraft pulping which is a chemical 

pulping process that uses a mixture of sodium hydroxide (NaOH) and sodium sulfide (Na2S) as 

the cooking liquor. Figure 2 is a general diagram of the kraft pulping process.

Figure 2. General Diagram of the Kraft Pulping Process (Smook 2002)
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Kraft pulping emissions sources include the digester, washer, evaporator, black liquor 

storage, knotter, screen, oxygen delignification, steam stripper, causticizing, and turpentine 

production systems. Each of these systems is comprised of several pieces of process equipment 

and multiple vents. Vent gas collection systems are used to transport emissions to a control 

device. Subpart S defines the following collection systems:

High volume, low concentration or HVLC system means the collection of equipment 

including the pulp washing, knotter, screen, decker, and oxygen delignification systems, 

weak liquor storage tanks, and any other equipment serving the same function as those 

previously listed.

Low volume, high concentration or LVHC system means the collection of equipment 

including the digester, turpentine recovery, evaporator, steam stripper systems, and any

other equipment serving the same function as those previously listed.

These collection systems are often referred to more generally as non-condensable gas (NCG) 

collection systems. The gas collection systems typically route the collected vent gases to a 

combustion unit such as a thermal oxidizer, lime kiln, recovery furnace, process heater, or boiler

for incineration-based control (destruction) of HAP emissions.

Based on our review of the Part I survey data, it is apparent that the actual configuration 

of NCG systems is mill-specific, and configurations are not constrained by the equipment listings 

in the definitions of “HVLC system” and “LVHC system” above. For example, some vents from 

an evaporator system (technically part of the LVHC system definition) may be collected in the 

HVLC system; or some pulp washing system vents (technically part of the HVLC system 

definition) may be collected in the LVHC system. Some mills do not refer to their systems as 

“LVHC” or “HVLC” but simply refer to their NCG collection system. Stripper off gases (SOGs), 

which are technically part of the LVHC system by definition, are also referred to separately and 

often have their own collection system. Regardless of how the collection system is configured or 

referred to, the end result of incineration-based control is the same. In this memorandum, for 

simplicity, we will refer to LVHC, HVLC, NCG, and SOG collection systems as the “NCG 

system.”

The most common incineration-based controls reported in the Part I survey for NCG 

systems included lime kilns, power boilers, thermal oxidizers, and recovery furnaces. Some mills 

reported use of scrubbing in conjunction with incineration-based control. In some cases, white 

liquor scrubbers are used prior to incineration to remove TRS from the emissions stream to be 

incinerated (to prevent sulfur dioxide [SO2] emissions). In other cases, a scrubber may appear 

after incineration-based control (e.g., as the boiler or lime kiln’s control device; or as an SO2

scrubber on a thermal oxidizer). A few mills reported use of scrubbers both before and after 

incineration-based control. In addition, 80 kraft mills reported use of backup controls for some 

portion of their NCG systems.

Digester systems. Continuous or batch digester systems are used for the chemical 

treatment of wood or non-wood fibers. Digester chip bins that pre-steam the wood chips may

operate under high or low pressure and are considered part of the overall digester system if, as 

defined in subpart S, the steam used is not fresh steam. Several chip bins pre-steaming wood 
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chips were noted in the Part I survey responses as being routed through the NCG system for 

incineration-based control (e.g., in a lime kiln, boiler, recovery furnace, or thermal oxidizer).

Other components of the digester systems include associated flash tanks, blow tanks, 

blow heat recovery accumulators, relief gas condensers, prehydrolysis units preceding the pulp 

washing system, and related equipment. These components are routed to incineration-based 

control through the NCG system, consistent with the control requirements under subpart S.

The practices, processes, and controls reported in the Part I survey responses for digester 

systems were consistent with those evaluated during MACT development. No new developments 

were identified.

Pulp washing systems. Pulp washing systems are part of the HVLC system and include 

all equipment used to wash pulp and separate spent cooking chemicals following the digester 

system and prior to the bleaching system, oxygen delignification system, or papermaking system 

(at unbleached mills). The pulp washing system equipment includes vacuum drum washers, 

diffusion washers, rotary pressure washers, horizontal belt filters, intermediate stock chests, and 

their associated vacuum pumps, filtrate tanks, foam breakers or tanks, and related equipment.

Controls reported in the Part I survey for kraft pulp washing included incineration-based 

controls typical of NCG systems. Process improvements noted by some mills included use of 

clean condensates (e.g., stripped condensates) or fresh water on the last stage of pulp washing.

These types of process improvements and controls were previously identified and evaluated 

during the original MACT development.

As part of the HVLC system, pulp washing system vent gases are eligible for use as 

emissions averaging debits under the clean condensate alternative (CCA). As discussed in a 

separate memorandum, 38 mills used the CCA as part of their MACT compliance strategy. (EPA 

2011c)

No new developments in practices, processes, or controls were observed for pulp washing 

systems.

Evaporator systems. Evaporator systems include equipment associated with increasing 

the solids content and/or concentrating spent cooking liquor from the pulp washing system. Preevaporators, multi-effect evaporators, concentrators, and vacuum systems, as well as associated 

condensers, hotwells, and condensate streams, and similar equipment are all part of the 

evaporator system.

Evaporation systems are part of the LVHC system defined in subpart S. Controls reported 

in the Part I survey for evaporator systems included NCG collection and incineration-based 

control. Some mills reported use of a scrubber-incineration control configuration (as also noted 

above for other equipment routed through the NCG system). No process controls specific to 

evaporator systems were reported. 
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No new developments in practices, processes, or controls were revealed in the Part I 

survey responses for evaporator systems.

Knotter and screen systems. Knotters remove knots, oversized material, or pieces of 

uncooked wood from the pulp slurry after the digester system and prior to the pulp washing 

system. The knotter system equipment includes the knotter, knot drainer tanks, ancillary tanks, 

and related equipment. Screens remove oversized particles from the pulp slurry prior to washed 

stock storage for bleaching or papermaking. Knotter and screen systems may be combined such 

that there is no vent in between systems.

The kraft pulping vent gas emission limits apply for all knotters and screens at new 

sources, and existing knotters and screens above certain total HAP levels (0.1 pounds [lb] of total 

HAP per ton of oven dried pulp [ODP] for knotters; 0.2 lb/ton ODP for screens; and 0.3 lb/ton 

ODP for knotters and screens). According to the Part I survey results, many knotters and screens 

are not vented, or a fugitive emission sources vented into a building. Vent gases for other 

knotters and screens are collected in the NCG system and incinerated.

No new developments in practices, processes, or controls were observed for knotters and 

screens.

Deckers. Deckers are used to thicken the pulp slurry or reduce its liquid content after the 

pulp washing system and prior to high-density pulp storage. The decker system includes decker 

vents, filtrate tanks, associated vacuum pumps, and related equipment. The kraft pulping vent 

gas emission limits apply for all new deckers and existing deckers using any process water other

than fresh water or paper machine white water, or that use any process water with a total HAP 

concentration (measured as methanol) greater than 400 parts per million by weight (ppmw).

The Part I survey results indicated that most deckers are either uncontrolled (e.g., 

operating with fresh or white water) or are routed to the NCG system for incineration, consistent 

with the requirements of subpart S. A couple of mills noted, in general, that their foul condensate 

collection practices reduce emissions associated with process water (and as a result emissions 

from equipment using process water would be reduced, including the decker).

No new developments in practices, processes, or controls were observed for deckers.

Liquor storage. Spent pulping liquor is generated when cooking liquor is separated from 

the pulp during washing. Spent liquor contains dissolved organic wood materials and residual 

cooking compounds. After concentration in the evaporator system, this spent liquor (e.g., kraft 

black liquor) is a valuable fuel that is burned in the chemical recovery furnace. In addition to 

producing steam, the recovery furnace is where the process of reclaiming the residual inorganic 

cooking compounds begins. Kraft recovery furnaces are subject to a different MACT standard

(subpart MM) and are not discussed further in this memorandum.

Spent liquor storage consists of various tanks (or, in rare cases, liquor ponds). Strong 

liquor storage tanks contain liquor that has been concentrated (through evaporation) in 

preparation for combustion or oxidation in the recovery process. Weak liquor storage tanks 
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(other than washer filtrate tanks) contain spent liquor recovered from the pulping process prior to 

the evaporator system. Weak liquor storage tanks are considered part of the HVLC system and 

are subject to the pulping vent gas standards for new kraft pulping lines. Strong (or heavy) liquor 

storage tanks are not subject to the pulping vent gas limits.

Most liquor tanks were reported as fugitive, vented into a building, or otherwise 

uncontrolled. Some weak, strong, and intermediate liquor tanks were reported as being vented to 

the NCG system for incineration control. One mill reported used of black liquor temperature 

control (to minimize flashing) but did not indicate how the temperature control was achieved. No 

other process changes specific to liquor storage HAP emissions were noted. Ten kraft mills 

reported use of liquor ponds, most likely temporary emergency storage areas used to capture 

spills or leaks, which can be inferred since these same ten kraft mills also reported use of a series 

of spent liquor storage tanks. Liquor ponds are fugitive emissions sources. 

In sum, no new developments in practices, processes, or controls beyond NCG collection 

and incineration control were identified for liquor storage.

Oxygen delignification. Oxygen delignification is subject to the kraft pulping vent gas 

standards for new and existing pulping lines. Oxygen delignification uses oxygen to remove 

lignin from pulp after high-density stock storage and prior to the bleaching system. The oxygen 

delignification system equipment includes the blow tank, washers, filtrate tanks, any interstage 

pulp storage tanks, and any related equipment. 

Based on review of the Part I survey results, most oxygen delignification systems are 

vented through the NCG system to incineration-based control. A few oxygen delignification 

systems are not vented, some are included as a debit generated source under the CCA, and a few 

are subject to site-specific MACT provisions or equivalency by permit.

No process controls were noted. No new developments in practices, processes, or 

controls were identified for oxygen delignification.

Condensate strippers. Condensate strippers are most commonly steam strippers. Steam 

stripper systems contain a column used to remove compounds from wastewater or condensates 

using steam, stripper feed tanks, condensers, or heat exchangers, and (if present at the mill) 

equipment associated with a methanol rectification process including rectifiers, condensers, 

decanters, storage tanks, and related equipment. Steam stripper system vents are commonly 

controlled through collection and incineration of the SOG.

No new developments in practices, processes, or controls beyond SOG collection and 

incineration control were identified for condensate strippers. However, as discussed in a separate 

memorandum pertaining to kraft condensates, the HAP removal efficiency of steam strippers is 

expected to have improved since promulgation of subpart S. (EPA 2011a)

Causticizing. In the kraft pulping process, smelt exiting from the recovery furnace is 

causticized to remove impurities left over from the furnace and to convert sodium carbonate 

(Na2CO3) into active NaOH. The causticizing procedure begins with the mixing of smelt with 
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“weak” liquor to form green liquor, named for its characteristic color. Contaminant solids, called 

dregs, are removed from the green liquor, which is mixed with lime (CaO). After the lime 

mixing step, the mixture, now called white liquor due to its new coloring, is processed to remove 

a layer of lime mud (CaCO3) that has precipitated. The primary chemicals recovered are caustic 

(NaOH) and Na2S. The remaining white liquor is then used in the pulp cooking process. The 

lime mud is treated to regenerate lime in the lime kiln calcining process. (EPA 2002)

Figure 2 shows the kraft pulping process with chemical recovery, including the 

causticizing loop. The principle equipment in the causticizing loop include:

 Equipment handling green liquor (e.g., green liquor clarifiers, green liquor storage tanks, 

dregs washers) 

 Slaker (and associated slaker grits handling equipment)

 Causticizer tanks

 White liquor clarifier and storage tanks

 Lime mud washer, precoat filter (thickener), and associated weak wash tanks

Lime kilns are covered under a separate MACT standard (i.e., subpart MM) for chemical 

recovery combustion sources.

According to the Part I data base, no add-on controls are used for green liquor processing.

Green liquor tanks were mostly uncontrolled fixed roof tanks, though there are a few open tanks

(some of which are in a building). Several mills reported that their green liquor processing 

equipment is a source of fugitive emissions (i.e., not vented through a conveyance). Process 

techniques that may reduce HAP were reported, including use of stripped condensates and 

makeup water derived from freshwater.

Particulate matter is generated from the strong reaction of the lime with green liquor in 

the slaker, which produces some steam. The steam carries PM with it as it is released out the 

vent. Slakers operate with some form of water spray scrubbing designed for PM control. Based 

on emission unit descriptions, it appears that some slakers and causticizers may vent through the 

same scrubber. Slakers (and causticizers) at one mill were reported to be vented to a scrubber 

and lime kiln, while the slaker at another mill was reported to vent to the LVHC collection 

system, where emissions are destroyed by a lime kiln. The effectiveness of slaker scrubbers at 

reducing HAP is limited. General process techniques reported that may reduce HAP from slakers 

and causticizers include use of stripped condensates and makeup water derived from freshwater.

Most lime mud handling equipment is uncontrolled. However, dust collectors (mainly

baghouses) were reported for some lime mud handling systems. One facility uses the lime kiln 

electrostatic precipitator (ESP) for PM control. Two facilities use the lime kiln wet scrubber for 

particulate control. Although no add-on controls specific to HAP are used for lime mud 

processing, use of fresh water or clean process water (i.e., water that is not contaminated with 

untreated condensates) is a process control measure in use by many facilities.

Add-on controls for weak wash handling are non-existent, with one exception. One weak 

wash storage tank was reported to be routed to HVLC and incinerated in a boiler. Of the weak 
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wash handling units that were reported, most of the tanks had a fixed roof. No process controls 

(beyond those mentioned above in general) were reported.

Most causticizers, white liquor clarifiers, and white liquor tanks are uncontrolled. Most 

tanks are fixed roof tanks, though some have an open roof (often located in a building). Some 

white liquor processing equipment was reported as a fugitive emission source. A few were 

reported to have a wet scrubber or mist eliminator, but it is not clear whether these scrubbers 

would have any effect on HAP emissions. In some cases, the slaker scrubber is used. General 

process techniques reported that may reduce HAP include use of stripped condensates and 

makeup water derived from freshwater.

Miscellaneous causticizing equipment includes equipment that could not be easily 

characterized based on the emission unit description provided in the ICR (or did not fit in the 

green liquor, lime mud, slaker, or white liquor groupings). Nearly all of this equipment is 

uncontrolled with the following three exceptions:

 A “Causticizer Receiver Tank” that operates with wet scrubber control

 A “MACT I Phase I Tank” that operates with scrubber and lime kiln control

 A “Recovery Accumulator” that is routed through the LVHC system for thermal 

oxidizer control

These equipment are believed to be unique and specific to the mill where they operate, and,

therefore, are not considered further in the technology review.

In general, causticizing equipment does not operate with HAP-reducing add-on controls 

(with the exception of a couple of random causticizing units tied into an NCG system). Process 

techniques reported that may reduce HAP emissions include use of stripped condensates as 

causticizing equipment makeup water or makeup water derived from freshwater. Use of process 

liquids including evaporator or recycled condensates was reported by some mills. Recycling of 

kraft condensates is one compliance option available to facilities that must meet the requirements 

of 40 CFR 63.446. However, most mills reporting use of condensates often reported use of such 

condensates along with fresh water as makeup to the causticizing system. Given the site-specific 

nature of condensate recycle practices (i.e., the extent to which treated vs. untreated condensates 

are reused), the lack of information on water flow rates and excess wastewater treatment plant 

capacity, and issues of fresh water availability, it would be extremely difficult to determine 

emissions reductions, costs, and impacts associated with changes to causticizing makeup water.

As noted above, kraft mills are already subject to the subpart S kraft condensate standards, which 

require condensates to either be treated or recycled to process equipment subject to the pulping

vent gas standards. Thus, reuse of contaminated condensates in causticizing equipment not 

subject to the vent gas standards is minimized by the existing kraft condensate standards. This is 

evidenced by the fact that post-MACT nationwide emissions from causticizing are low compared 

to other kraft pulping processes. Changes to the causticizing system were not explored further as 

part of the technology review for these reasons.

Turpentine production. Turpentine is often recovered as a byproduct from the digester 

gases at kraft pulp mills. Approximately 80 mills reported production of turpentine in response to 

the Part I survey. The turpentine recovery system includes condensers, decanters, storage tanks,

and related equipment. Turpentine recovery is part of the LVHC system at kraft pulp mills.
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No new developments in practices, processes, or controls beyond NCG collection and 

incineration were identified for turpentine recovery.

2. Soda pulping processes

Soda pulping is a chemical pulping process that uses NaOH as the active chemical in the 

cooking liquor. As shown in Table 1, LVHC system equipment at existing soda mills (digesters, 

evaporators, and steam strippers) is subject to the pulping vent gas standards in subpart S. In

addition, the pulp washing system at new soda mills is subject to the pulping vent gas standards 

in subpart S. One soda pulping mill operates in the U.S. This mill operates a steam stripper to 

reduce emissions associated with condensates, and routes all affected emission points including 

washers and several liquor storage tanks to its NCG system and a thermal oxidizer control.

No new practices, processes, or controls were identified for soda pulping.

3. Semi-chemical pulping processes

As defined in subpart S, semi-chemical pulping means a pulping process that combines 

both chemical and mechanical pulping processes. The semi-chemical pulping process produces 

intermediate pulp yields ranging from 55 to 90 percent. 

The major process difference between chemical pulping and semi-chemical pulping is 

that semi-chemical pulping uses lower temperatures, more dilute cooking liquor or shorter 

cooking times, and mechanical disintegration for fiber separation. There are two types of semichemical pulping processes currently in use—the neutral sulfite semi-chemical (NSSC) pulping 

process and the nonsulfur semi-chemical pulping process. The digestion step in the NSSC 

pulping process consists of heating pulp in sodium sulfite (Na2SO3) and Na2CO3. The digestion 

step in nonsulfur semi-chemical pulping consists of heating pulp in Na2CO3 alone or with NaOH.

A total of eight stand-alone semi-chemical pulp mills were reported in the Part I survey

(two NSSC mills and six nonsulfur semi-chemical mills). This is a declining segment of the 

subpart S category; there were 32 semi-chemical mills in operation at rule promulgation.

Secondary fiber pulps are now used in many of the same products as virgin semi-chemical pulp.

Semi-chemical pulping is often combined with secondary fiber pulp processing. Since secondary 

fiber pulping is essentially a recycle operation (and not a chemical pulping process), we 

considered mills that produce only semi-chemical and secondary fiber pulps to be stand-alone 

semi-chemical pulping operations.

The subpart S pulping vent gas standards for semi-chemical mills apply to the LVHC

system at existing sources and the LVHC system and pulp washing system at new sources.

Emissions from these systems are to be enclosed, vented to a closed-vent system, and routed to a 

control device that either (1) reduces total HAP emissions by at least 98 percent; (2) reduces total 

HAP at the thermal oxidizer outlet to 20 ppmv or less; (3) reduces total HAP emissions using a 

thermal oxidizer operating at a temperature >1600°F and a residence time >0.75 seconds; or (4) 

reduces total HAP emissions using a boiler, lime kiln, or recovery furnace.
14

Based on information in the Part I database, all semi-chemical mills are equipped with 

some type of system for collecting and venting NCGs. Most mills vent the collected emissions to 

boilers, although a couple of mills vent the emissions to lime kilns. One mill uses a combination 

of a condenser and packed-bed scrubber to meet the 98 percent limit. We identified no new 

practices, processes, or controls for pulping processes at semi-chemical mills.

4. Sulfite pulping processes

The sulfite pulping process relies on acid solutions of sulfurous acid (H2SO3) and 

bisulfite ion (HSO3

-

) as the cooking liquor. The bisulfate ion enters the process as a compound of 

the form M(HSO3

-

), where the “M” may be calcium (Ca), ammonia (NH3), sodium (Na), or 

magnesium (Mg). Six mills reported sulfite pulping processes in response to the Part I survey.

Three mills perform NH3-based sulfite, two perform Ca-based sulfite, and one mill is co-located 

with kraft pulping and performs Na-based sulfite pulping. There are no longer any Mg-based 

sulfite mills. Sulfite pulping is a declining segment of the subpart S category; there were 16 

sulfite mills in operation at rule promulgation.

The subpart S pulping vent gas standards for sulfite mills apply for digester, evaporator, 

and washer vent gases at existing sources. At new sources, the vent gas standards also apply for 

strong and weak liquor storage tanks, and acid condensate storage tanks. Acid condensate 

storage tanks store cooking acid following the SO2 gas fortification process used to generate 

H2SO3. Different numerical vent gas emission limits apply for Ca- and Na-based sulfite than for 

NH3 or Mg-based sulfite.

The HAP emissions at the Ca-based and NH3-based sulfite mills are typically collected 

and routed through a scrubber system. The HAP emissions from equipment at the co-located 

kraft and Na-based sulfite mill are controlled through the kraft LVHC system. No new practices, 

processes, or controls were identified for sulfite mills.

5. Pulp storage

All types of mills operate tanks, high density storage, stock chests, etc. to store pulp at 

various points along the pulp production line, prior to bleaching, or prior to papermaking.

Several pulp storage tanks are either not vented, fugitive sources, or vented inside a building.

Very few controls were noted for pulp storage in the Part I responses, with the exception of a few 

storage tanks that are connected with the mill’s NCG system (e.g., likely because they are part of 

a larger system with emission limits under subpart S). It was unclear from the descriptions 

provided in survey responses if the pulp storage may have been part of another system (e.g., 

some mills reported pulp storage for equipment that is part of the digester or washer system). No 

new process changes were noted for pulp storage.

6. Papermaking

Papermaking includes equipment used to convert pulp into paper, paperboard, or market 

pulp, including the stock storage and preparation systems, paper or paperboard machines, paper 
15

machine white water system, broke recovery systems, and the systems involved in calendering, 

drying, on-machine coating, slitting, winding, and cutting.

EPA previously (during original rule development) evaluated two undemonstrated 

control measures that could potentially reduce HAP emissions from papermaking: (1) removal of 

HAPs from the pulp stock and white water before the papermaking system (e.g., with a white 

water steam stripper); and (2) control of papermaking system vent streams through vent gas 

collection and incineration. Analysis of these control options concluded that there are no 

demonstrated methods for removing HAPs from the pulp stock or white water and that applying 

HAP control to the vent streams of papermaking systems is not cost-effective (Air Docket A–95–

31, IV– B–8 [ERG 1997a]). Technical challenges noted with these two control options included 

fiber clogging of the steam stripper columns and heat exchangers, and the extremely high air 

flow rates from paper machines to be treated with incineration controls.

The EPA also investigated the use of HAP-containing additives in papermaking systems, 

the magnitude of HAP emissions resulting from the use of papermaking system additives, and 

the viability of a MACT standard based on additive substitution. It was concluded that additives 

did not contribute significantly to HAP emissions from the paper industry, with only 20 percent 

of the HAP additive content emitted to air, while the remaining 80 percent remained in the paper 

product or white water. The industry-wide total annual HAP emissions attributable to additives 

were estimated to be around 50 tpy, and were considered negligible in comparison to the industry

pre-MACT baseline emissions of over 200,000 tpy of total HAPs. EPA also noted that 

papermaking chemical and additive suppliers are continually working to reduce the HAP content 

of additives, but that it was not clear from available information that substitution options are 

technically feasible for all products. Therefore, EPA concluded that a standard for papermaking 

systems based on low-HAP additive substitution was not warranted at the time of promulgation 

in 1998. (72 FR 18525-18526, April 15, 1998 and Air Docket A–95–31, Item IV–B–6 [ERG 

1997b]).

As part of the current technology review, the Part I ICR data along with BACT 

determinations for papermaking were examined to determine if there have been developments in 

practices, processes, or controls applicable to papermaking systems since subpart S promulgation 

in 1998. (RTI 2011b) The only available measures for reducing papermaking HAP emissions 

include process changes or work practices (e.g., practices relating to VOC in papermaking 

additives). Add-on controls for HAP emissions have not been put into practice and remain 

undemonstrated.
16

III.References

EPA 2002 U.S. Environmental Protection Agency Office of Compliance. Profile of the 

Pulp and Paper Industry, 2nd Edition. EPA/310-R-02-002. November 2002.

EPA 2003 U.S. Environmental Protection Agency. Pulp, Paper, and Paperboard Industry –

Background Information for Proposed Air Emission Standards; Manufacturing 

Processes at Kraft, Sulfite, Soda, and Semi-Chemical Mills. Document No. EPA453/R-93-050a. Research Triangle Park, NC. October 1993.

EPA 2011a J. Bradfield and K. Spence, EPA. Memorandum to Docket EPA-HQ-OAR-2007-

0544. Summary of Kraft Condensate Control Technology Review. October 23, 

2011

EPA 2011b J. Bradfield and K. Spence, EPA. Memorandum to Docket EPA-HQ-OAR-2007-

0544. Summary of Pulp Bleaching Technology Review. November 17, 2011

EPA 2011c J. Bradfield and K. Spence, EPA. Memorandum to Docket EPA-HQ-OAR-2007-

0544. Summary of Clean Condensate Alternative Technology Review. October 

20, 2011

ERG 1997a Memorandum from C. Leatherwood, Eastern Research Group (ERG), to P. 

Lassiter, U.S. EPA. September 10, 1997. Maximum Achievable Control 

Technology (MACT) Determination For Papermaking Systems. Air Docket A–

95–31, IV–B–8.

ERG 1997b Memorandum from C. Leatherwood, ERG, to E. Manning, EPA. March 11, 

1997. Analysis of Papermaking System Additives. Air Docket A–95–31, IV–B–6.

NCASI 2010 National Council for Air and Stream Improvement. Compilation of ‘Air Toxic’ 

and Total Hydrocarbon Emissions Data for Pulp and Paper Mill Sources – A 

Second Update. Technical Bulletin No. 973. February 2010.

ICR 2011 Pulp and Paper ICR Data.

RTI 2011a Memorandum from T. Holloway and C. Gooden, RTI, to J. Bradfield and B 

Schrock, U.S. EPA. September 30, 2011. Summary of RBLC and Other Findings 

to Support Section 112(d)(6).

RTI 2011b Memorandum from V. Hanzel, RTI, to J. Bradfield and B Schrock, U.S. EPA.

August 2, 2011. Papermaking Technology Review Information Received from 

State Contacts.

Smook 2002 Smook, G. Handbook for Pulp & Paper Technologists. 3

rd Edition. Angus Wilde 

Publications Inc., Bellingham WA. 2002. 
17

Table 1. Summary of MACT I and III (Subpart S) Standards

Source limit details

Typical source control 

systems Gaseous organic HAP standard

Kraft pulping vent gases:

Existing sources: LVHC system1; 

knotter or screen (above HAP 

cutoffs), pulp washing, decker 

(using contaminated water), and O2 

delignification.

New sources: Same as existing, 

except applies for all knotters, 

screens, and deckers plus weak 

liquor storage tanks.

Route through a closed vent 

collection system to a 

boiler, lime kiln, recovery 

furnace, or thermal oxidizer

(1) Reduce total HAP emissions by ≥98 wt%; 

or

(2) Reduce total HAP concentration at the 

outlet of thermal oxidizer to ≤20 ppmv @ 

10% O2 (dry basis); or

(3) Reduce total HAP emissions using a 

thermal oxidizer operating ≥1600°F and

≥0.75 sec residence time; or

(4) Use a boiler, LK, or RF in which the HAP 

gas stream in introduced with the primary 

fuel into the flame zone; or

(5) Use a boiler or RF with a heat input 

capacity ≥150 MMBtu/hr (44 MW) in which 

the HAP gas stream is introduced with the 

combustion air.

Soda or semichemical pulping vent 

gases:

Existing sources: LVHC system1

New sources: Same as existing, plus 

pulp washing system.

Route through a closed vent 

collection system to a 

boiler, lime kiln, recovery 

furnace, or thermal oxidizer

(1) Reduce total HAP emissions by ≥98 wt%; 

or

(2) Reduce total HAP concentration at the 

outlet of thermal oxidizer to ≤20 ppmv @ 

10% O2 (dry basis); or

(3) Reduce total HAP emissions using a 

thermal oxidizer operating ≥1600°F and 

≥0.75 secs residence time; or

(4) Use a boiler, LK, or RF in which the HAP 

gas stream in introduced with the primary 

fuel into the flame zone; or

(5) Use a boiler or RF with a heat input 

capacity ≥150 MMBtu/hr (44 MW) in which 

the HAP gas stream is introduced with the 

combustion air.

Sulfite pulping vent gases:

Existing sources: Digester vent, 

evaporator vent, and pulp washing.

New sources: Same as existing, plus 

strong and weak liquor storage 

tanks, and acid condensate storage 

tanks.

Route through a closed vent 

collection system to a 

scrubber or other control 

device (emission limits 

apply to combined 

emissions from vents, 

control device wastewater, 

and condensates)

(1a) Ca- or Na-based:

Emit total HAP (as methanol) ≤0.89 lb/ton 

ODP, or

(1b) Ca- or Na-based: Reduce total HAP (as 

methanol) by ≥92%;

(2a) NH3- or Mg-based: Emit total HAP (as 

methanol) ≤2.2 lb/ton ODP, or

(2b) NH3- or Mg-based: Reduce total HAP 

(as methanol) by ≥87%.
18

Source limit details

Typical source control 

systems Gaseous organic HAP standard

New and existing bleaching vent 

gases: Chlorine bleaching systems, 

kraft/sulfite/soda bleaching with any 

chlorinated compounds, and 

mechanical/secondary fiber/nonwood bleaching with ClO2.

Route through a closed vent 

collection system to a 

caustic scrubber or similar 

device

(1) Reduce total chlorinated HAP (except 

chloroform) limit: ≥99 wt%, or

(2) Meet ≤10 ppmv of total chlorinated HAP 

(except chloroform) at control device outlet, 

or

(3) Meet ≤0.002 lb total chlorinated HAP 

(except chloroform)/ton ODP at control 

device outlet.

(4) Work practice for chloroform - either 

meet effluent guidelines or use no 

hypochlorite or chlorine for bleaching.

Kraft pulping process condensates 

(process liquids) from digester, 

turpentine recovery, evaporator, 

LVHC system1, and HVLC system 2

(some exceptions)

Route through a closed vent 

collection systems to 

pulping equipment

(1) Reduce total HAP emissions by ≥98 wt%; 

or

(2) Reduce total HAP concentration at the 

outlet of thermal oxidizer to ≤20 ppmv @ 

10% O2 (dry basis); or

(3) Reduce total HAP emissions using a 

thermal oxidizer operating ≥1600°F and

≥0.75 secs residence time; or

(4) Use a boiler, LK, or RF in which the HAP 

gas stream in introduced with the primary 

fuel into the flame zone; or

(5) Use a boiler or RF with a heat input 

capacity ≥150 MMBtu/hr (44 MW) in which 

the HAP gas stream is introduced with the 

combustion air.

Route to biological 

treatment/steam stripper or 

other control device

(1) Reduce total HAP ≥92 wt%; or

(2a) For mills without bleaching, remove 

≥6.6 lb total HAP/ton ODP, or

(2b) For mills without bleaching, meet ≤210 

ppmw total HAP at control device outlet; or

(3a) For mills with bleaching, remove ≥10.2 

lb total HAP/ton ODP, or

(3b) For mills with bleaching, meet ≤330 

ppmw total HAP at control device outlet.

Clean condensate alternative (CCA) 

is an emissions averaging approach 

to offset emissions from certain 

existing kraft pulping sources.

Install and operate clean 

condensate alternative 

technology.

Emissions reductions from CCA ≥ emissions 

reductions achieved through kraft pulping 

HVLC system standards

1The LVHC system includes digester, turpentine recovery, evaporator, and steam strippers.

2The HVLC system includes pulp washing, knotter, screen, decker, O2 delignification, weak liquor storage tanks.
19

Table 2. Nationwide HAP Emissions from the Subpart S Source Category 

Reported in Part II of the 2011 ICR

HAP Category Name Nationwide HAP emissions, tpy

Methanol 38,650

Acetaldehyde 2,029

Cresol/Cresylic Acid (Mixed Isomers) 758

Phenol 454

Chloroform 356

Formaldehyde 274

Hydrochloric Acid 259

Biphenyl 218

Hexachloroethane 207

Xylenes (Mixed Isomers) 137

Propionaldehyde 135

1,2,4-Trichlorobenzene 129

Methylene Chloride (Dichloromethane) 120

Acrolein 101

Carbon Disulfide 90

Cumene 83

Toluene 82

Styrene 77

Tetrachloroethylene (Perchloroethylene) 75

Methyl Isobutyl Ketone (Hexone) 61

Acetophenone 60

Hexane 56

Carbon Tetrachloride 40

Trichloroethylene 37

Benzene (Including Benzene From Gasoline) 25

Naphthalene 24

Chlorine 24

1,1,2-Trichloroethane 23

Methyl Chloroform (1,1,1-Trichloroethane) 22

Ethylbenzene 18

Vinyl Acetate 16

Chlorobenzene 15

Methyl Chloride (Chloromethane) 14

Hexachlorocyclopentadiene 10

Vinylidene Chloride (1,1-Dichloroethylene) 8

Glycol Ethers 7

Acetonitrile 5

Ethylene Dichloride (1,2-Dichloroethane) 4

Vinyl Chloride 4

Triethylamine 3

Carbonyl Sulfide 3

Acrylonitrile 3

Chloroacetic Acid 2

Pentachlorophenol 1

Ethylene Glycol 0.8

Diethanolamine 0.8
20

HAP Category Name Nationwide HAP emissions, tpy

Cyanide Compounds 0.7

1,3-Butadiene 0.5

2,4,5-Trichlorophenol 0.4

Methyl Bromide (Bromomethane) 0.3

Nickel Compounds 0.2

Acrylamide 0.2

Ethylene Dibromide (Dibromoethane) 0.1

Nitrobenzene 0.1

Antimony Compounds 0.1

Lead Compounds 0.1

Propylene Dichloride (1,2-Dichloropropane) 0.1

2-Nitropropane 0.05

Toluene-2,4-Diamine 0.02

Methyl Iodide (Iodomethane) 0.02

Chromium Compounds 0.02

Ethylidene Dichloride (1,1-Dichloroethane) 0.01

Bromoform 0.01

Cadmium Compounds 0.01

Beryllium Compounds 0.01

2,4,6-Trichlorophenol 0.01

Polycyclic Organic Matter as 15-PAH 0.01

Manganese Compounds 0.01

Catechol 0.01

N,N-Dimethylaniline 0.005

Mercury Compounds 0.004

Arsenic Compounds(Inorganic Including Arsine) 0.004

Selenium Compounds 0.004

Dibutyl Phthalate 0.003

1,4-Dichlorobenzene 0.003

Chlorobenzilate 0.002

Cobalt Compounds 0.002

Bis(2-Ethylhexyl)Phthalate (Dehp) 0.001

Polycyclic Organic Matter as non-15 PAH 0.001

Polycyclic Organic Matter as 7-PAH 0.001

1,1,2,2-Tetrachloroethane 0.001

Ethylene Oxide 0.0003

Aniline 0.00001

Total 44,726