DATE: July 11, 2015 

SUBJECT: History of Flue Gas Desulfurization Use in United States- 1970-1976 

FROM: Mike Laney, RTI International 

TO: Rulemaking Docket ID: EPA-HQ-OAR-2013-0495 

The purpose of this memorandum is to present background information on the use of flue gas 

desulfurization (FGD) scrubbers by the electric utility industry in the early 1970s in the U.S. and 

to describe the influence that environmental legislation and regulations had on their use. The 

information in this memorandum is excerpted from a 2001 doctoral student dissertation.1

Pre 1970 Clean Air Act Amendments 

The earliest FGD device used by an electric power plant was installed in 1926 at the Battersea 

Power Station in London, England. The alkaline water from the Thames River provided most of 

the reagent for the device. Lime/limestone scrubbing emerged in the United States in the 1950s 

when the Tennessee Valley Authority (TVA) conducted small-scale and limited pilot-plant 

studies. The first major plant work in the United States appears to have been that of Universal 

Oil Products (UOP) at a Wisconsin utility installation beginning in 1965. In 1966, Combustion 

Engineering, in conjunction with National Dust Collector Riley Environeering, tested a system 

involving boiler injection of limestone, followed by scrubbing, in a pilot unit at a Detroit Edison 

power plant. The first commercial installations of this process in boilers larger than 100 MW 

occurred in St. Louis, Missouri, and Lawrence, Kansas, in 1968. The pilot installation of this 

process demonstrated SO2 removal of 98 percent at a stoichiometric limestone-to-SO2 ratio of 

1.1 to 1. Initial designs revealed a number of problems, including pluggage, and the design was 

then changed so that limestone was no longer introduced directly into the boiler but rather into 

slurry recycle tanks. This change improved the reliability of the system, although it resulted in 

lower SO2 removal efficiencies. (McIlvaine, 1990) 

Although the U.S. FGD equipment and services industry had its start in the years before 1970, 

significant growth did not occur in this industry until after 1970. By the late 1960s, however, 

there was enough interest in FGD technology that the first SO2 Control Symposium was held in 

1969. This conference continued to convene regularly and became a major agent of knowledge 

transfer in the SO2 industrial-environmental innovation complex. 

1970 Clean Air Act Amendments 

The 1970 Clean Air Act Amendments (1970 CAA), signed on December 31, 1970, divided the 

sources of SO2 emissions into two categories – existing and new – and directed the newly created 

 

1

 Margaret R. Taylor, The Influence of Government Actions on Innovative Activities in the Development of 

Environmental Technologies to Control Sulfur Dioxide Emissions from Stationary Sources, A dissertation submitted 

to the Carnegie Institute of Technology, Carnegie Mellon University in partial fulfillment of the requirements for the 

degree of Doctor of Philosophy in Engineering and Public Policy, Pittsburgh, PA, January 2001. 
Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards 

(NAAQS) for criteria air pollutants, including SO2. The EPA promulgated NAAQS on the first 

five criteria air pollutants in April 1971. The NAAQS for SO2 were set at values of 0.14 parts per 

million (ppm) averaged over one day, and 0.03 ppm averaged over a year. 

The 1970 CAA required that, within nine months of the promulgation of a NAAQS, each state 

submit to the EPA a State Implementation Plan (SIP) setting out how the state would achieve and 

maintain the NAAQS for existing sources. Upon approval of a SIP by EPA, it became 

enforceable as both state and federal law, with penalties up to $25,000 per day and up to one year 

in prison for each SIP provision violation (Bryner, 1995, p.101; Findley and Farber, 1992, p. 

103). Under the SIP program, SO2 emissions from existing sources that contributed to violations 

of primary NAAQSs were to be eliminated by 1975-77. Thus, the SIP program became an 

important regulatory force for reducing SO2 emissions from existing power plants and other 

sources. 

For new sources, the 1970 CAA directed the EPA to set nationally unified performance 

standards for major categories of stationary sources including fossil-fuel fired steam electric 

generators. Section 111 of the 1970 CAA required the EPA to set new source performance 

standards (NSPS) based on “best system of emission reduction which (taking into account the 

costs of achieving such reduction), the Administrator determines has been adequately 

demonstrated (Ackerman and Hassler, 1981, p. 11).” In December 1971, the EPA set 

performance standards for SO2 emissions from new and modified steam generators with a heat 

input greater than 250 million British Thermal Units (MBTU) per hour. The NSPS for SO2 set a 

maximum allowable emission rate of 1.2 pounds of SO2 per MBTU of heat input. This standard 

was based on an SO2 removal efficiency of 70 % when combusting the high-sulfur eastern coals, 

which had a sulfur content of about 4 pounds of SO2 per MBTU heat input. Alternatively, plants 

could burn low-sulfur coals (about 0.7% sulfur or less) and still achieve the NSPS emission 

level. However, such low-sulfur coals were generally available only in the western U.S. and not 

readily available to most coal-fired power plants at the time. 

In addition to the 1970 CAA, two other important legislative developments occurred in 1970-76 

period that had implications for SO2 control. First, in response to the Arab oil embargo of 

October 1973 and the resulting U.S. energy crisis, the Energy Supply and Environmental 

Coordination Act (ESECA) was passed in June 1974 to promote the use of domestic coal over 

foreign oil. It reauthorized the 1970 CAA for another year while allowing suspensions of final 

clean air standards until January 1, 1979, provided that primary NAAQS would not be violated 

(Bailey, 1998, p. 182). The second important development arose from court challenges to the 

1970 CAA. In one of these cases, Fri v. Sierra Club 412 US 541 (1973), the Supreme Court 

agreed with environmentalists that the EPA could not approve SIPs that permitted the 

degradation of areas of air that were cleaner than the 1970 CAA minimum standards. In response 

to this decision, in 1974 the EPA issued “prevention of significant deterioration” (PSD) 

regulations that divided all clean air areas of the country into three categories based on their 

levels of industrial development. 

While multiple options were available to utilities for SO2 compliance in the 1970-76 time period, 

EPA promoted scrubbing in part due to perceived difficulties associated with the alternative 
options of switching to low-sulfur western coal, chemical coal cleaning, fluidized bed 

combustion (FBC), solvent refined coal, and low-BTU gasification. However, in addition to 

scrubbing for SO2 control, EPA continued to support technologies such as physical coal cleaning 

and the blending of low- and high-sulfur coals, which were considered sufficient control methods 

for plants facing modest reductions. In addition, between 1973 and 1976 the EPA removed their 

support for tall stacks and other supplemental control systems that primarily dispersed SO2 

(Gage, 1976; Quarles Jr. et. al., 1974; Train, 1976). 

In support of FGD technology, the EPA engaged in multiple research, development, 

demonstration, and technology facilitation activities during this time period, including the 

following: 

• Funding the TVA to prepare cost estimates of various FGD processes. Because 80 

percent of TVA’s generation came from a number of high-sulfur coal burning steam 

plants first constructed in the late 1940s, it had a strong interest in SO2 control strategies 

(McCraw, 1976; Durant, 1985). 

• Establishing the Shawnee test facility in April 1972. In cooperation with TVA and the 

engineering firm Bechtel, this facility, equipped with three 10 MW boilers, provided 

invaluable operating data on scrubbing, beginning with lime/limestone systems (Quarles 

Jr. et. al., 1974). 

• Beginning its financial commitment to the SO2 Control Symposium, a technical 

conference that continues today. 

• Contracting with PEDCo-Environmental Consultants, Inc. to evaluate the status of FGD 

technology in the U.S. These FGD evaluations continued into the late 1980s (Devitt, 

Isaacs, and Laseke, 1976). 

• Engaging in cooperative research and demonstration activities with utility/vendor teams. 

In 1975, the EPA signed a Memorandum of Understanding with the Electric Power 

Research Institute (EPRI, founded in 1973) to facilitate sharing of technical information 

and cooperation of R&D project (Gage, 1976). 

• Conducting SO2 control research in the late 1970s as a result of the 1974 Federal 

Nonnuclear Energy Research and Development Act that provided the legislative 

authorization for the EPA’s energy/environmental control technology program 

(Zimmerman et. al., 1980). 

Growth in FGD Market 

The 1970 CAA and the 1971 NSPS were flexible regarding the technological alternatives for 

attainment for both existing and new sources of SO2, and a number of technological strategies 

were pursued during this time. The stringency of the NSPS and the limited availability of coal 

emitting less than 1.2 pounds of SO2 per MBTU, however, provided a particularly strong 

incentive for the development of FGD technology. The tight deadline for attainment of primary 

SO2 emissions standards – May 31, 1975 – also provided a profit incentive for FGD vendors to 

expand their commercial capabilities. 

By the time of the promulgation of the SO2 NSPS in 1971, only three commercial scrubber units

were operating on power plants in the United States. The next five years, however, saw the total 

number of commercial scrubber units grow by a factor of ten. In order to understand the market 
forces operating on the SO2 industrial-environmental innovation complex, it is important to keep 

in mind the 1970 CAA division of sources into the categories of “existing” and “new and 

modified.” In general, “new” FGD units accompany the construction of new coal-fired utility 

boilers, while “retrofit” FGD units are constructed on existing boilers. Figure 1 shows the 

number of new utility-operated coal-fired steam turbine units brought online between 1970 and 

1976. This is the market background for new FGD units, particularly after the 1971 NSPS. 

Figure 2 shows the total number of commercial FGD units brought online between 1973 and 

1976, broken down into the categories of new and retrofit construction. By comparing the two 

datasets underlying these figures, it appears that 10% of the new coal-fired boilers brought online 

between 1973 and 1976 had new FGD units. Retrofit FGD technology accounted for 72% of 

total FGD unit installation between 1973 and 1976 and was thus the driver of the utility FGD 

market. This is despite the construction of significant numbers of new coal-fired boilers after the 

1971 NSPS and despite the fact that retrofit technology was generally 25 - 30% more expensive 

than new technology during the 1970 - 76 period (Ackerman and Hassler, 1981, p. 135). 

Figure 1. Number of new utility-operated coal-fired steam turbine units in 1970-76. 

Source: Adapted from Energy Information Administration (1996) 

Notes: The year of commercial operation is the year that control of the unit was turned over to 

the dispatcher. Includes all units active since 1970. 

Figure 2. U.S. scrubber market, 1973-76 

Source: Adapted from Soud (1994) 

The predominant type of FGD technology in 1970-76 was lime/limestone wet scrubber, but some 

utilities had begun to investigate less expensive spray dryers. In addition, a few commercial 
regenerable processes were installed in the early 1970s (Devitt, Isaacs, and Laseke, 1976; 

McIlvaine, 1990). According to a 1976 overview of FGD technology by PEDCo- Environmental 

Consultants, Inc., SO2 removal efficiencies ranged from 40 to 90% during the 1970 to 1976 

period. FGD technology had been installed during this period on units varying both in size – 

from 30 MW to 800 MW – and in the sulfur content of coals consumed. The PEDCoEnvironmental Consultants, Inc. overview also noted that (1) more systems were being installed 

to meet state standards that are more stringent than NSPS levels, and (2) more systems are being 

installed on low sulfur coal vs. high sulfur coal applications. 

 

The number of vendors of scrubbers increased greatly during the 1970-76 period and throughout 

the 1970s. In 1971, only one scrubber vendor was in the utility FGD market. By the end of the 

1970s, sixteen U.S. firms supplied FGD systems to utilities, as did the U.S. government agencies 

of TVA and the Department of Interior’s Bureau of Mines. Several foreign firms also served the 

U.S. utility FGD market by the end of the 1970s. 

Scrubber Operational Issues 

The R&D being conducted by SO2 industrial-environmental innovation complex in the 1970-76 

period focused in large part on the reliability problems experienced by scrubber users. Table 1 

summarizes the major reliability problems of scrubbers operating during this period, as detailed 

in an important EPA hearing on power plant compliance with SO2 air pollution regulations. In 

addition to the problems listed in the table, sludge disposal was widely recognized as a 

significant problem (Quarles Jr. et. al., 1974, p. 51). 

TABLE 1. Observed Technical Problems in Early Scrubbers 

Source: Testimony at hearing on power plant compliance with SO2 regulations conducted 

between October 18, 1973 and November 2, 1973 by the EPA (Quarles Jr. et. al., 1974, p. 35) 
According to PEDCo-Environmental Consultants, Inc., by 1976, performance of units had 

improved to the point that the average operability of scrubber units ranged from about 80 - 95% 

depending upon the system and the averaging period (Devitt, Isaacs, and Laseke, 1976, p.24).

Other technological improvements were in increased limestone utilization and sludge oxidation 

for more effective waste disposal. The TVA reported in 1976 on some of the lime and limestone 

technological developments that had recently occurred. These changes included sludge fixation; 

a growing tendency for utilities to increase scrubber redundancy and sparing as insurance for 

reliability problems; the use of spray towers in place of mobile-bed scrubbing devices; and 

measures to promote increased operating reliability (McGlamery et. al., 1976, p. 88). 

Besides changes in scrubber design, EPRI, which had started its own R&D program for FGD in 

1974, called on the utility industry to institute changes in scrubber operations. To maximize 

reliability, EPRI stated that “utilities must assume responsibility to make the scrubber system 

work.” According to EPRI, assuming responsibility meant having a qualified staff of “chemists 

as well as mechanical and chemical engineers,” not depending on process guarantees and fixedcost contracts, and giving “the scrubber operating and maintenance priority equal to all other 

power station systems (Nannen and Yeager, 1976, p. 112).” 

In summary, the 1970-76 period was one of great activity in the SO2 industrial-environmental 

innovation complex. As the SO2 control market grew rapidly, many firms either entered the 

utility FGD market or acquired existing entrants. FGD vendors, as well as utilities – particularly 

through EPRI – initiated R&D efforts during this time period. The technological successes of 

both public and private R&D helped to improve equipment reliability, limestone utilization, and 

waste disposal in the 1970-76 period. Still, a considerable amount of progress in FGD 

technology was to occur. Despite initial reliability problems and low SO2 removal efficiencies, 

Figure 3 and Figure 4, demonstrate how quickly SO2 control technologies diffused and improved 

as a result of innovative activities that occurred inside the black box of the SO2 industrialenvironmental innovation complex, as supported and spurred on by government actions. 

FIGURE 3. Improvements in SO2 Removal Efficiency of Commercial FGD systems as a 

Function of Cumulative Installed FGD Capacity in the U.S. 
Source: Based on data from Soud (1994), Energy Information Administration (1999) 

Figure 4 provides an estimate of FGD capital cost reductions as a function of FGD GWe capacity 

(based on Soud, 1994; McGlamery et. al., 1980; Laseke, Jr. et. al., 1982; Keeth, Ireland, and 

Moser, 1986; Keeth, Ireland, and Radcliffe, 1990; and Keeth, Ireland, and Radcliffe, 1991. 

Capital cost reductions were minimal in the 1976 to 1980 time period during which SO2 removal 

efficiencies improved rapidly. Steeper improvements in capital costs occurred only after steep 

improvements in SO2 removal efficiencies (capital costs improved greatly between 1980 and 

1990, while removal efficiencies improved rapidly between 1976 and 1980). Capital costs 

leveled out in the 1990s, although to a lesser extent than removal efficiencies. 

FIGURE 4. Reductions in Capital Cost of a New Wet Limestone FGD System for a 

Standardized Coal-fired Power Plant (500 MWe, 3.5% sulfur coal, 90% SO2 removal) 

Source: Based on Soud, 1994; McGlamery et. al., 1980; Laseke, Jr. et. al., 1982; 

Keeth, Ireland, and Moser, 1986; Keeth, Ireland, and Radcliffe, 1990; and Keeth, Ireland, and 

Radcliffe, 1991.

Patent Analysis 

In the previous sections, the innovation in SO2 control technologies in the early 1970s and the 

improvements that took place in these years with respect to SO2 removal efficiencies and capital 

costs were described. Patent activity as an indicator of inventive activity and innovation, can be 

used to demonstrate the influence of government action on the SO2 industrial-environmental 

innovation complex. Patenting activity as a measure of inventive activity has not only been used 

by many studies to gauge inventive activity, but also speaks to the marketing strategies of firms 

that can lead to adoption and diffusion (for published reviews of patent research, see Archibugi 

and Pianta, 1996; Basberg, 1987; Griliches, 1990; Pakes and Simpson, 1989; Pavitt, 1985; 

Schankerman, 1989). 
Two different analyses of patent datasets support patenting activity as an indicator of the 

influence of regulation on inventive activity. One analysis, using a subclass-based dataset 

approach, demonstrated that, despite the existence of government legislation dating back to 1955 

that authorized research into air pollution abatement methods, patent activity in SO2 control was 

limited until after the introduction of a regulatory regime. Patent activity levels in this analysis 

can be portrayed as a step-function divided into two main periods by the 1970 CAA and its 

associated 1971 NSPS for power plants (which effectively mandated the existence of a national 

market for FGD in the U.S.). In the period before the 1970 CAA, no more than four patents were 

filed in a given year, while in the second period, 1971 to 1996, patenting activity never fell 

below a minimum activity threshold of seventy-six patents per year. Figure 5 displays the 

number of patents filed over time in SO2 control technologies. The more than ten-fold increase in 

patenting activity between 1967 and 1971 is the type of sudden large burst in patenting activity 

that suggests is certain to indicate a change in external events relevant to the patented 

technology. The analysis also demonstrated that patent activity in the 1971 to 1996 period 

peaked in the years 1978, 1979, 1988, and 1992. This pattern of peaks was also exhibited in the 

second, abstract-based patent dataset, analysis. These analyses as well as interview with subject 

matter experts support the idea that inventive activity, as measured by patents, is spurred 

temporarily by the existence and anticipation of government regulatory actions. 

FIGURE 5. U.S. Patents Relevant to SO2 Control Technology as Identified with the 

Patent Subclass Method 

Policy Implications 

This work has shown that the existence of national government regulation for SO2 emissions 

control stimulated innovation. The patent analysis in this dissertation shows that national 

regulation is a more effective stimulant of inventive activity than national legislation in support 

of air pollution abatement research alone, with no regulatory requirements. A second policy 

implication of this work is that regulatory stringency appears to be particularly important as a 

driver of innovation, both in terms of inventive activity and in terms of the communication 

processes involved in knowledge transfer and diffusion. 
Increased regulatory stringency may have helped stimulate the formation of communication 

channels important to knowledge transfer in the diffusion of SO2 control technology. The 1979 

NSPS, which was more stringent and affected a larger number of utilities than the 1971 NSPS, 

thereby creating a larger market for FGD in the U.S., coincided with the growth in crossaffiliation paper co-authorship in the conferences held between 1979 and 1995. In addition, it 

corresponded with the beginning of a major increase in the number of papers that were presented 

and the number of organizations and authors that presented at the SO2 Symposium. All of these 

findings about the effects of regulatory stringency on innovation appear to be related to the 

finding in the mainstream innovation literature that demand is a major driver of innovation. The 

findings in this dissertation about regulatory stringency and innovation may be especially 

relevant to policymakers considering a new national regulatory regime for a pollutant for which a 

dominant environmental control technology has not been established. (The history of the 

development of environmental controls for mercury emissions from coal-fired power plants are a 

great example of this relationship between regulatory stringency and innovation.) 

A third policy implication of this work is that inventive activity, as captured by patents, is 

spurred temporarily by the existence and anticipation of government regulatory actions. This 

temporary spurt in inventive activity thus provides a brief burst in the stock of the public good of 

knowledge from which new discoveries and innovations (especially in SO2 control technology) 

draw. 

A second stand-alone finding of this work that is relevant to policy-makers is the determination 

that as electric power generation doubles, the operating and maintenance costs of FGD systems 

decline to 83% of their original level. This finding, which is very much in line with progress 

ratios determined in other industries, shows that quantifiable technological improvements can be 

shown to occur solely on the basis of the experience of operating an environmental control 

technology forced into being by government actions. 

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