evaluating alternatives for controlling organic solvent

Evaluating Alternatives for Controlling Organic Solvent Emissions fiom Tray Dryers

Marc Karoll' and Ramon U

The public, governments at all levels, and international agencies are focusing attention on organic solvent emissions as a principal cause of the increased levels of ozone and smog in ambient air worldwide. Pharmaceuti- cal tray-drying operations can potentially result in the re- lease of large quantities of solvents, and it is likely that American and international regulations governing these emissions will tighten in the 1990s. This article presents technical, economic, and regulatory evaluations of several pollution-control alternatives.

ray dryers are commonly used in the pharmaceutical industry T to remove the liquid medium from blended wet-solid granulations. Inexpensive organic solvents often are used as the liquid medium in these granulations. and during drying the solvents result in emissions of volatile organic compounds (VOCs) into the atmosphere. The nature of VOC emissions from tray dryers - very high emission rates of a dilute stream at the beginning of a run followed by a sharp decline as drying progresses - poses both technical and regulatory problems for the pharmaceutical industry. At the same time, VOC emissions are being more strictly regulated because of concerns regarding ozone and smog. This article reviews common pollution- control technologies such as condensation, gas absorption, carbon adsorption, and incineration, in terms of their feasibility in reducing VOC emissions to allowable levels. These assessments are made from both technical and economic points of view.

Mixing multiple-component solids into a uniform blend and crys- tallizing and purifying intermediates or final products involves the use of solvents. Water is not appropriate for many applications, however, so inexpensive organic solvents such as isopropanol (IPA), toluene, and naphtha are used. Before the final granulation or product can be sold, solvent must be completely removed. Evaporation is the most convenient method. Commonly, the solvent-laden solids are placed

M.n K a d and Ramen U are project engineers for the environmental engineering and consulting firm of Malcolnt Pirnie, Inc., P.O. Box 75Ib White Plains. NY 10602, USA. tel. (914) 694-2100,

on trays that are loaded onto racks and are wheeled into room-sized ovens. These ovens are generally operated at 140-180 OF for long pe- riods of time (8-48 h or longer). Such a rigorous drying process is necessary because FDA standards forbid the presence of any organic solvent in the final product.

Tray-drying operations can result in a significant amount of solvent emissions. After being drip-dried, wet-solid granulations typically contain 1.0 Ib of liquid solvent for every 6.0 Ib of total wet solids, although this ratio can vary. Even small ovens used in the pharmaceutical industry may be loaded with as much as loo0 Ib of wet solids and emit 150-200 Ib of organic solvents into the atmosphere during a batch run.

To establish a profile of VOC emission rates, a material balance test was conducted using a small-to-medium-sized o\en to dry a wet pharmaceutical granulation. The oven was loaded with approximately 948 Ib of wet solids that contained approximately 141 Ib of isopropanol. VOC emissions were estimated by differential weighing every half hour of 12.59 of the total trays used. Results from an actual run are shown in Figure I : a second run showed a very similar profile.

As Figure I shows, the solvent-emission rate is not constant through- out the drying cycle. Rather. the solvent content of the wet granulation decreases in a nearly exponential fashion and is influenced by the oven temperature and exit-air flow. Generally, 40-509 of the total solvent in the granulation is evaporated and emitted during the first hour of the drying cycle. Pollutant-emission rates are commonly expressed in pounds per hour, and Figure 2 shows the data from Figure 1 expressed as uncontrolled emission rates of VOCs.

U.S. REGUWORY ASPEM In the United States, one of the most protracted environmental problems in many areas is ground-level smog. which is a heterogeneous ' mixture formed by the photochemical reactions of volatile organic chemicals and nitrogen oxides in ambient air. One of the more dele- terious components of smog is ozone, an unstable compound that has documented adverse health effects. Dangerous smog levels are indi- cated by measured ambient ozone concentrations. The United States Environmental Protection Agency has ruled that if the concentration of ozone in ambient air exceeds 0.12 ppm more than one day per year, the area is not in attainment with federal standards for ambient ozone. Currently, more than half of Americans live in regions that are nonattainment for ozone.

To reduce ambient ozone levels, the U.S. Congress enacted the Clean Air Act authorizing states to promulgate regulations aimed at reducing emissions of VOCs and nitrogen oxides. In the 1970s the goal was to achieve compliance with ozone standards nationwide. How- ever, regulations affecting VOC emissions grew more complex in the 1 no,-- ~ ~ ~ .~ .*'-. . L - - P . . - ~~ , ~' - A ~ > ~

their dislike of brand-name companies using the distress of the generics industry as an op- portunity to further attack generics' market presence. At an open meeting of the Blue Rib- bon Committee on Generic Medicines cre- ated by GPIA, Peck complained about the proliferation of challenges akainst ANDAS. He termed most of these filings frivolous and base attempts by brand-name firms to protect their own markets. In a remark directed at PMA, Dingell declared at the Waxman hearing that lobbying for a wider bill only helps "those in the brand-name industry who, for their own greedy ends, wish to prolong the pain for the generic-drug industry."

However the legislative battle turns out, pharmaceutical companies u ~ l l only draw increased congressional scrutiny to themselves by trying to parlay the generics industry problems into a wholesale challenge to product equlvalency, which, overall. has proven to be a respectable way to produce less expensive and therefore highly desirable alternatives to many branded products. W

Such objections don't carry much weight at CDER, where officials are fed up with what they see as a lie-low-till-it-blows-over attitude among m n y generics producers. For example, at the June Pharmaceutical Update '90 conference sponsored by the Food and b u g Law Instiate in Washington, one p e r - ics trade association attorney insisted that what was needed to correct the industry's problems was more resources to help FDA move along drug approvals - not punitive legislation for industry. In voicing objections to Dingell's legislation. generics companies and trade associations argue vehemently that a manufacturer should not be penalized for the isolated malfeasance of an individual em- ployee. rejecting the notion that the buck stops at the desk of the CEO.

FDAer; would like someone to take respon- sibility. Jerussi complained to NAPM that he hasn't seen a complete submission in the 13 months since he uas transferred over to generic drugs. Burlington told the same group that the main problem with genencs was an "abandonment by companies of a commit- ment to mahe good medicine." It was only "a

B R A N D - W E VS. GENERICS At the 28 June hearing on the Dingell legislation held by Waxman's health subcommit- tee. the prime complaint from the Generic Pharmaceutical Industry Association (GPIA), NAPM, and some generics firms about Din- gell's legislation was that it singled out generics companies and did not impose similar penalties on brand-name companies. A Din- gel1 staffer countered that although the corn- mittee had found some GMP violations among major brand-name manufacturers, it did not unearth any pattern of illegal behav- ior on the scale of that found in the generics industry. Despite this. the Pharmaceutical Manufacturers Association (PMA) has maintained stiff opposition to the measure because it could set an unattractive precedent for future action against brand-name firms. The PMA solution to prevent problems uith generics approvals in the future IS for FDA to require more information in ANDAs to prove that the generics are safe and effective.

Only Mylan Laboratories and Barr Labo- ratorles broke ranks uith their colleagues and supported the bill as a way to restore public

One thing Dingell and FDA agree on I >

f C 8 -{ \ E 20- - z s: T i i O - r-” 0 0.5 110 1.5 210 2.5 310 3.5 410 4.5 510 5.5 6;O 6.5 7IO

Time (h)

Nut@ 1: Profile of VOC emissions during a drying cycle.

, ment for ozone. Because of this, federal, state, and local authorities have intensified their enforcement efforts. The imminent reauthori- zation of the Clean Air Act (expected this year) will undoubtedly spur the passage of even more stringent regulations at the state and local levels. Nearly every state and many local districts currently have laws that regulate VOC emissions from general sources. Some regulations

tions specific to the pharmaceutical industry or to VOC emissions from batch-type operations such as tray dryers.

The regulation that is most applicable to tray-dryer operations requires total VOC emissions to be limited to 33 Ib/day (or per batch).

:.. .. ._ .

-. --- are geared to specific industries, and a number of states have regula- .... .. .. .

70

60

50

9 1

40

‘E 30 0

0 .- ::

P 20

10

0. 1 . 2 3 4 5 s i

Drying-cycle time (h)

Table I: S ta t e s that regulate total VOC emissions on a batch basis.

Alabama Indiana North Carolina Arizona Kentucky Ohio California Louisiana Pennsylvania Colorado Maryland Tennessee Connecticut Michigan Texas Delaware Missouri Wisconsin Georgia New York

unless the batch contains more than 330 Ib, in which case at least 90% control of batch emissions must be achieved. The latter is normally the case for most tray-drying operations, which means in practice that 90% control of the potential daily (or batch) emissions must be achieved. At least 20 states have enacted codes identical or similar to this (see Table I).

Some locales limit VOC emissions on an hourly basis or on both an hourly and daily basis. If the hourly emission limit (typically 3-9 Iblh) is exceeded, a specified VOC control efficiency (ranging from 70% to 95%) must be maintained during that time span. Under this type of regulation, even emissions from small dryers must be controlled. This type of regulation is enforced in the District of Colum- bia, New Jersey, Puerto Rico, and Virginia.

Figure 2 indicates that operations of even small dryers will result in VOC emissions that are greater than the limits stated in either type of regulation. As a result, practically every pharmaceutical tray-dryer oven that handles organic solvents in states u i t h specific VOC regulations would require control of solvent emissions. In addition, air permits must be obtained from state and/or local pollution-control agencies.

VOC EMISSION-CONTROL OPTIONS Maintaining tray-dryer operations in compliance with VOC regulations is a difficult job for environmental or plant engineers because of the stringent requirements of the regulations and the fact that most of the emissions occur in a short period of time (the first few hours of the drying run). A number of related factors - including cost, space, energy demand, reusability of recovered solvent, costs of dis- posing of solvent if it cannot be reused, and ability to control different potential pollutants - make the choice of control options very difficult. Adequate time should be invested in making this important and potentially expensive selection.

A number of devices have been used successfully to control VOC emissions. Although no single control device can satisfy all regulatory, operational, and economic requirements, the options that are available offer distinct advantages and disadvantages. Therefore, control options must be selected on the basis of the site-specific needs of the process and of the pharmaceutical firm.

Conds&ion. In practice, organic vapors can be condensed to the liquid state by extraction of heat. Common surface condensers are designed to allow optimal surface area for vapor cooling and collection of condensate. Most condensers are of the shell and tube type wherein the coolant flows on the shell side, lowering the temperature and thereby condensing the organic vapors that flow inside the tubes.

The degree to which organic vapors can be controlled in a condenser is proportional to the vapor pressure of the pollutant. Greater control is achieved as the vapor pressure drops, which is accom- plished by decreasing the temperature. The temperature in the condenser, in turn, is determined by the coolant used; typical coolants

Flgw, 2: VOC emissions from Figure I expressed as uncontrolled emission rates during a drying cycle.

92 Pharmaceutical Technology MARCH 1991

S u R E-TE M P __ ~~

CONTROLLED ENVIRONMENT EQUIPMENT

Controlled Environments in Pre-fabricated Modular Rooms to Fit a Wide Variety of Applications.

Pharmaceutical Hospital Clinical Industrial Research Blood Storage Plant Growth Cold Rooms Warm Rooms

Wrth more than 35 years experience behind Sure-Temp designs, you are assured of dependable performance for your critical requirements. Call or write today for our catalog and planning guide.

1-800-247-8399 You Can Be Sure with Sure-Temp!

SURE-TEMP 1 144 S. SAUNDERS STREET

RALEIGH, NC 27603 .

S.. US at INTERPHEX booth 248 cirrle 74

I.

heat exchanaers For the c.---

pharmkeuticol industry Shell and t u b e exchangers since 1926. Features designed spe- cifically to m e e t your needs. Stainless steel, ultra-polished fin- ish, fully drainable, easily cleanable, sanitary fittings, milled h e a d s , crevice free. Double tubesheet with tubes seal-welded and rolled into double serrated holes. ASME Code s tamped and FDA standards. Sizes 4 to 60 inches in diameter to 40 feet.

FREE CATALOG AND ENGINEERING ASSISTANCE.

yula 330 Bryant Avenue, Bronx. New York 10474 corporation (21 2) 991-0900. Fax (212) 842-4239

include cool tap water (which can lower the vapor temperature to 60- 80 "F); chilled water (final temperature of 35-45 "F); and chilled gly- col, brine, or refrigerant (final temperature of -80 to t 2 0 OF).

Gas absorption. The gas-absorption process controls emissions by promoting the contact of organic vapor with a liquid medium capable of absorbing it. A gas absorber's control efficiency depends on the surface area exposed, residence time, solubility of the vapor in the liquid, and the degree of chemical reaction. Gas-absorption equipment is designed to provide thorough contact between the media in order to permit interphase diffusion of these materials.

Some common absorbers include packed towers, plate towers, and venturi scrubbers, all of which increase gas-liquid contact by dispers- ing the liquid in the vapor-laden vessel. Packed towers, which pro- mote absorption by means of inert solid packing material, provide the longest residence time of any gas absorber type and are preferred for vapors with low solubility. Mass transfer is maximized in counter- current tower operation.

Another common gas absorber type is plate towers. Plates in the tower disperse the vapor into many small gas bubbles, increasing vapor interfacial area, which thus allows greater absorption by the liquid. This is the preferred method when low liquid rates are required or when dilute pollutant streams must be treated.

Venturi scrubbers optimize contact between vapor and liquid by in- troducing the gas stream into the liquid at high velocity. The liquid is then atomized into small droplets that, by baffling, disperse through- out the free space of the chamber. maximizing liquid contact with the vapor. The high speed of the vapor stream reduces residence time and increases the contact surface area. Venturi scrubbers are more often used to control particulates but have been used in some applications to control organic vapors.

Carbon adsorption. In the carbon-adsorption process. orpanic molecules adsorb onto activated carbon. which is an excellent medium for organic adsorption because of carbon's affinity for organic molecules and its large surface area for adsorption. The organics can be desorbed and recovered. after which the carbon can be reused.

Most systems are designed to pass the organic-laden airstream down- ward past a fixedgranular carbon bed. In multibed units, the most common type used, one carbon bed is in operation adsorbing organic vapors while the other bed is regenerated (commonly with steam) to remove adsorbed organics. If the organics removed are water-soluble. then an aqueous solution is obtained for disposal. If the organics are insoluble or slightly soluble, an oily organic phase is recovered for treatment or disposal. The aqueous phase may contain some organic residue and must be properly disposed of. This usually involves ob- taining new waste-water discharge permits.

Carbon adsorption is most useful when the organic concentration of the airstream is high and recovered compounds can be reused. Car- bon adsorption systems must be well designed and monitored to mini- mize and detect contaminant breakthrough.

Intinerution. Another major approach to organic-vapor control is incineration. the high-temperature oxidation of hydrocarbons to carbon dioxide and water. The two major types of incineration are thermal and catalytic.

Thermal oxidizers or afterburners expose the solvent-laden stream to temperatures above the solvent's autoignition point. Given sufficient time, complete oxidation will occur. Generally. the combustion temperature is maintained at a minimum of 1200 "F and an average of approximately 1500 OF. The residence time is maintained in the range of 0.5-1 .O s in order to obtain a destruction efficiency of 90- 99%. Another factor affecting destruction efficiency is adequate mixing of the solvent stream in the chamber.

Although the oxidation of organics releases heat, auxiliary fuel is usually necessary to maintain the required temperatures if solvent concentrations are insufficient. Heat recovery is a viable option because

94 Pharmaceutical Technology MARCH 1891

HOLLAND-McGINLEY CO. P.O. Box 57, Malvern, PA 19355

0 TABLET COMPRESSION TOOLING -when consistent quality is required and you need to talk to someone with real experience, call us.

0 TOOLING MAINTENANCE CLASSES -when you need to have all your questions answered while learning how to handle, maintain and repair your tooling, do like the majority of U. S. pharmaceutical companies do, contact us.

0 MAINTENANCE SUPPLIES -when you want the most extensive line of motors and supplies available from a single source, call us.

Hardness Testers, Storage Cabinets, Ultrasonic Cleaning Units and More.

To receive literature or to talk to

call 215-647-7382 or fax 215-296-8779 Gdo 77 Jack McGinley

Cake from vibrating plates. The BHS Pressure Plate Filterdelivers clear filtrate and dry cake discharge automatically.

Unique, vibrating-discharge design eliminates the wear and tear associated with rotating shafts and stuffing boxes. Cake can be washed, extracted, steamed or dried before discharge. Wet, sticky cakes, too. The vapor-tight vessel contains hazardous materials, with no operator exposure.

Holland Avenue, Papack, NJ 07977. 2L?1/234-1000. Ask for Bulletin BHS Plate. ..

For clear filtrate, hands-off, talk to Kom/ine-Sandefson,

Agents lor BHS. Werk Sonthofen. West Germany. ~- - _ _

the temperature of the flue gas is high. Waste heat may be used to preheat the solvent-laden stream or even to help heat the drying oven.

Catalytic oxidizers control organic emissions via the same oxidation reactions as in thermal oxidation systems, but here VOC decomposi- tion occurs on a catalytic bed that usually contains platinum or pal- ladium. A major advantage of catalysis is that it requires a much lower temperature for oxidation than does a thermal system. Accord- ingly, catalytic oxidizers operate at 600-800 O F with a residence time of 0.3-0.5 s. As a result, catalytic systems require less supplemental fuel than do thermal systems. However, for catalysis to be effective, the stream must be free of substances that can poison the catalyst, as well as particulate matter that can plug and reduce the effective surface area. Other problems include disposal of spent catalyst and the high cost of replacing catalytic units.

TECHNICAL FEASIBILITY This section presents a feasibility analysis of each control technology and provides an economic analysis as appropriate. The following sim- plified example facilitates comparisons.

Let us assume a single drying oven that dries a number of pharmaceutical products and for which the worst-case batch of wet solids contains 400 Ib of an organic solvent that must be totally evaporated. The oven is operated at 150 O F , and it is assumed that during the initial (peak) hour of operation 200 Ib of VOCs are emitted. With an oven- exit volumetric flow rate of 6000 acfm, the evaporated solvent exits the oven quickly, allowing the solvent concentration within the oven to stay well below the lower explosive limit (LEL). The LEL fre- quently requires dilution of the airstream. however, which in practice makes VOC control more difficult. These conditions approximate those of a small-to-medium-sized industrial dryins oven. The assumed regulatory limit is 90% control of the total VOC in the batch. To reach this goal, 90% control during the peak hour must be a criterion.

Condensotion. Condensers are effective in reducing emissions of vapor streams with high solvent concentrations. As discussed earlier. solvent control is a function of reduced vapor pressure. If the contaminant in the airstream is pure. the condensate may be recovered and reused. In this example, IPA will be the model solvent.

To determine the condenser operating conditions, the IPA inlet concentration to the condenser must first be calculated. In this example, 200 Ib qf IPA in an hour corresponds to an evolution of 25.2 acfm of IPA. The mole fraction of IPA entering the condenser is: 25.2/ 6OOO = 0.004. Assuming a design of 90% control of the peak-hour emission rate, the mole fraction of IPA must be reduced to 0.0004. To reach the vapor pressure for a saturation mole-fraction of 0.0004. a temperature of approximately -40 O F must be maintained in the condenser. As a consequence, the energy expenditure required to maintain this temperature precludes the use of condensation.

In fact, condensers are not recommended for most industrial tray- drying applications because of the very low temperatures needed to condense 909 or more of the organic vapor in the stream, the resulting high energy cost required to maintain these temperatures, the potential for water freezing in the condenser tubes, and condensate- disposal problems if the condensate cannot be reused.

A surface condenser operated under high pressure, however, does increase the saturation pressure and thereby reduces the system's temperature requirement. In addition, a surface condenser using cooling water may be useful upstream of other control devices, particularly if the oven exit temperature is not optimal for the operation of the main control device. For example, condensers may be used to pre- cool oven gases and to reduce moisture in activated-carbon systems.

Abrorption. A packed tower with a once-through water system can

- 96 Pharmaceutical Techndogy MARCH 1991

effectively reduce emissions of water-soluble organics, such as IPA, to meet regulatory requirements. Wet scrubbers can easily reduce IPA emissions by more than 90% at loads of 200 Ibh or more. One dis- advantage of wet scrubbing an IPA-laden stream is the cost of dis- posing the IPA-laden water. Modifications to existing waste-water discharge permits may be required.

Based upon the example provided in this section, wet scrubbing is a candidate as a control device because IPA is highly soluble in water. To achieve 90% or greater control of IPA during peak load, a packed tower with sufficient packing height (typically 10 ft) can be operated to optimize IPA-water contact. Generally, 15-20 gal. of water or more are required for every 1000 ft3 of exhaust gas in order to achieve >90% control.

Scrubbers are not effective in removing water-insoluble organics, such as toluene. Although scrubbing with a nonvolatile organic, such as mineral oil, may be used. the process is inefficient and expensive, particularly at low solvent concentrations. Mineral oil would have to be reused to be cost-effective; however, desorption of absorbed solvent is prohibitively expensive, so wet scrubbing of a solvent such as toluene is not a feasible alternative.

Carbon adsorption. Activated carbon can effectively reduce solvent emissions from tray dryers if the system is properly designed and maintained. Problems that may hinder solvent adsorption include the presence of particulates, water, or water-solvent azeotropes in the inlet stream. Within the oven, the granulation should be covered to mini- mize particulate entrainment and the resulting fouling of the activated carbon. Reasonable action should be taken to reduce the humidity of the inlet stream. Lowering the inlet temperature (e.g., by using a surface condenser) is useful. Because the carbon adsorption process is exothermic. fire precautions should be taken. The carbon bed temperature should be monitored, and automatic sprinkler systems should be provided.

Removal of IPA using activated carbon is not cost-effective because IPA has a low adsorptive capacity. Large systems would be required to remuve the necessary amounts of IPA or other water-soluble solvents from typical industrial tray-oven applications.

Compared to PA, toluene can be more efficiently controlled by carbon adsorption because of carbon's affinity for toluene's larger, non- polar molecule. A dual-bed system would allow regeneration of one unit during operation of the other. If the oven has a large enough down- time, then a single bed can be employed. Using an adsorption efficiency of 7 Ib of toluene per 100 Ib carbon and a requirement of 909 control of the 400 Ib of toluene in the batch:

100 Ib carbon 5143 Ib carbon - 360 Ib toluene controlled per batch 7 lb toluene - per batch

A bed containing 6000 Ib of carbon should be used for this application.

The bed should be steam-regenerated shortly after the drying cycle has ended because of the high temperatures in the system. Because approximately 10 Ib of steam per 1.0 Ib of adsorbate is suggested, at least 3600 Ib of steam would be required for each drying cycle. Although the toluene and water form different phases, the water may contain up to 500 ppm of toluene and must be disposed of properly: waste-water disposal permits must be updated. M inbration. The main advantage of thermal incineration com-

pared to other control txhnologies is its ability to reduce the emissions of even low-concentration solvent streams. Control efficiencies in excess of 998 have been achieved for well-designed and well- maintained afterburner units. Incinerator size depends directly on the volumetric flow rate of the inlet airstream and the required residence time. In the example given, the design volume of 100 ft3 is obtained, based upon 6OOO acfm and 1 .O-s average residence time.

The energy required to operate a thermal incineration unit is estimated from the heat load required to raise and maintain the airstream temperature to the combustion temperature in the incinerator, assuming negligible solvent heating value. Thermal incineration is energy intensive, and it is common to bum auxiliary fuel to maintain the proper combustion temperature, although heat recovery, in the form of preheating the inlet stream or heating the drying oven itself, can reduce this energy cost.

In terms of regulatory compliance. thermal incineration offers the major advantage of high control efficiencies. With theoretical control efficiencies in excess of 999, afterburners are unlikely ever to become obsolete if existing regulations are changed to require greater control efficiency.

btaty)ic incineration. Like the thermal incinerators, catalytic incinerators can produce VOC control efficiencies greater than 999. The advantages of catalytic systems over thermal units include reduced auxiliary fuel requirements, smaller unit sizes, and reduced need for high- temperature materials of construction. Economically, the normal operating temperature of the process (600-800 OF) allows some heat recovery. However, the cost of the catalyst and its replacement after fouling add t? the operating cost. Annualized capital and operating costs of thermal and catalytic incinerators are presented in the following section.

Table lk Economic comDarison of emission-control alternatives (6000 acfm).'

I

Alternative

Total Installed

cost ( x $1000)

P a c k e d tower (once-through water) 90 Carbon adsorpt ion w/solvent recovery 275 Thermal incineration ~150% h e a t recovery 300 Catalvtic incineration w/50% h e a t recoverv 350

Annualized Capital cost

27 83 90

105

( x $1 0OO)t

Annual Operating

cost ( x $1 OOO)*

28 45

100 60

Total Annualized

cost

55 128 190 165

( x $1000)

- ~ - ~~ ~ ~~ ~~

'Costs presented in December 1989 dollars. TAnnualized capital cost is 30% of total installed cost, which includes depreciation at 10%; interest at 11%; taxes, insurance, and

administrative charges at 4%; and maintenance and labor at 5%. Wnnual operating costs based on 4000 h/year of operation; electricity at $O.lO/kwh; natural gas at $0.6O/therm; water at $1/1000 gal.;

carbon at $3/lb; steam at $8/1000 Ib; and labor at $20/h.

c .*

1

I

.- .. . . .

... . . ... . .

!

1

I I i i ! !

I

High Speed GMP Rotary Press JcMcO For Small To Medium Production Run.

The Machine Her Following Features:

1 . Die Table Driven by

2. Pre-compression and Final Compression;

3. Easy Changeover & Reduced Cleaning Time;

4. Accepts Standard iPT/EU Tooling;

5. Reasonably Priced

Main Shaft;

Available in 16.20 and 24 Stations.

USA REPRESENTATIVE PHARM EQUIPMENT CO. 1-800-347-3264

JENN CHIANG MACHINERY CO., LTD. P.0.EOX 391 FENG-YUAN, TAIWAN R.O.C. TELEX: 58349 SUNGS FAX: 88645437545

S.r US crt INl€RPncX-USI '91 booth 1252 Ckle 81

11 GUARANTEED 11 LABEL ~ ~ ~ ' 1 REMOVAL

ELIMINATE HAZARDOUS SOAKING CHEMICALS & HAND-HELD RAZORBLADES

The patented Hurst Label Stripper removes pressure sensitive and gummed labels at speeds to 600/Hr. Quick change tooling permits bottle sizes to 250 ML.

In summary, incineration is not very cost-effective for combustion of large volumes of air with low heat content, Le., air with a low concentration of combustible solvents. Drying ovens tend to operate at a highly aerated state to prevent-the combustible concentration from approaching the LEL. Thus, unless a facility operates a number of very large ovens, incineration is not an economical method, though it is a technically effective method, for control of solvent emissions from tray dryers.

ECONOMIC FEASIBILITY The total annualized costs. including capital and operating costs, of the various control technologies are presented in Table 11. Annualized capital costs are 30% of total installed costs (which include depreciation, interest, taxes, insurance, and administration), maintenance, and labor. Annualized operating costs include power, fuel, water, carbon replacement, steam, and labor costs.

Packed towers are, in general, the most economical control option for removing water-soluble organics such as IPA, and these systems allow removal efficiencies in excess of 95%. Carbon adsorption is the preferred method for controlling water-insoluble organics such as toluene. Applications that may warrant incineration include large operations involving several ovens or sources that emit varying amounts of different solvents simultaneously.

CONCLUSION The need to control solvent emissions from tray-drying processes is a fact of life for all pharmaceutical firms because of the high VOC emission rates and the increasing stringency of environmental regulations and the rigor of enforcement. Selecting the appropriate control technology depends upon regulatory rmissian requirements: site- specific utilities and space constraints: capital and operating costs: waste-disposal requirements: and system reliability and maintenance requirements. Choosing the most appropriate control device raises is- sues of regulatory compliance, efficiency of operation, and minimiz- ing costs: clearly, these choices must be made only after a number of factors have been examined closely. W

Medical discoverers honored The National Health Council and the Pharmaceutical Manufactur- ers Association (PMA) have honored five scientists with the Medi- cal Research Award to Outstanding Medical Discoverers. Hon- orees include: David W. Cushman, PhD, Bristol-Myers Squibb Co.; co-Nobel laureate Gertrude B. Elion. Burroughs Wellcome Co.: Howard J . Schaeffer, PhD, Burroughs Wellcome Co.: Hugh 0. McDevitt, MD, Stanford University School of Medicine; and Allen C. Steere, MD, New England Medical Center. The award acknowledges the scientists' contributions to medical science and public health. For more information, contact Mark E. Grayson, PMA, I 1 0 0 Fifteenth Street NW, Washington. DC 20005, USA. tel. (202) 835-3468.

Company noto 0 Janssen Pharmaceutica (Piscataway, New Jersey) has acquired Cyclex (Los Altos, California), which holds a coexclusive license, with sublicensing rights, covering the pharmaceutical use of hy- droxypropyl-P-cyclodextrin. With the acquisition of Cyclex and access to its patent, Janssen, a division of Johnson & Johnson, is capable of providing worldwide patent licenses on the use of hydrox ypropy l-P-cyclodextrin.

M o w in Batch Fluid-Bed Processiniz

U

Dilip M. Parikh

I Significant amounts of solid materials are processed using fluid-bed

, I i

I j( i

'1 i I I i i

technology. Suspension and movement of particles in an airstream maximizes the exposure of particle surfaces to air or gas, producing effi- cient evaporation. The primary factor influencing a fluidized-bed process is airflow. To understand and manipulate processing in a fluid bed, it is important to learn how airflow is generated, conditioned, and distributed through the bed during drying, agglomerating, and coating. This article describes how uncom- mon pressure drops and related processing problems can be identi- fied and rectified by studying the airflow of the system.

he batch fluid-bed processor is used T to perform drying, agglomeration, mixing, and coating operations. In the last 30 years, the popularity of the fluid-bed processor has expanded as manufacturers have provided different ways to control airflow through the unit. Sophisticated controls, com- puter systems that monitor process parameters, and air handlers equipped with temperature and humidity controls are some of the innovations that have increased the range of applications for batch fluid-bed processing. Figure 1 shows the typical components of a fluid-bed processing unit.

TYPES OF FLUIDIZED BEDS A fluidized bed is a bed of solid particles with a stream of air or gas passing upward through the particles at a rate great enough to set them in motion.

An expanded bed is formed when the gas or airflow rate increases and particles move apart. A few visibly vibrate and move about in restricted regions. At still higher velocities of airflow, all the particles become sus-

Pirrp M. Pu& is manager, process technology, at Aeromatic Inc.. 9165 Rumsey Road, Columbia, MD 21045, USA, tel. (301) 997-7010.

pended. At this point, the frictional force between a particle and air balances the weight of the particles, the vertical component of the compressive force between adjacent ~articles disappears, and the pressure drop through any section of the bed approximates the weight of air and particles in that section. The bed is referred to as an incipienrly fluidized bed or a bed at minimum fluidization. This is illustrated by Figure 2. With an increase in airflow rates beyond minimum fluidization, large instabilities with bubbling and channeling of air create different types of beds (Figure 3 ) .

A slugging bed is a fluid bed in which air bubbles occupy entire cross sections of the vessel and divide the bed into layers.

A boiling bed is a fluid bed in which the air or gas bubbles are approximately the same size as the solid particles.

A channeling bed is a fluid bed in which the air (or gas) forms channels in the bed through which most of the air passes.

A spouting bed is a fluid bed in which the air forms a single opening through which some particles flow and fall to the outside. At higher airflow rates, agitation becomes more violent and the movement of solids becomes more vigorous. Additionally, the bed does not expand much beyond its volume at minimum fluidization. Such a bed is called

i an aggregative or bubbling fluidized bed (Fig- ure 4). At sufficient airflow rates, the termi- nal velocity of the solids is exceeded, the upper surface of the bed disappears, entrainment becomes appreciable, and the solids are carried out of the bed with the airstream.

1 I

!

EFFECe OF AIRFLOW THROUGH THE BED As the air travels through the particle bed, it imparts unique properties to the bed. For example, the bed behaves like a liquid. It is pos- sible to propagate wave motion, which cre- ates the potential for improved mixing. The surface area of fluidized particles is large, which improves heat transfer, reduces process time, and imparts reproducible operating parameters. In a bubbling fluidized bed, no temperature gradient exists within the mass of the fluidized particles. This isothermal prop- erty results from the intense particle activity in the system. Thus, the fluid bed can be used to agglomerate particles, improve flow properties, instantize the product, produce coated particles, pellets, or tablets, taste- mask bitter products, or effect uniform chemi- , - cal reactions in a controlled fashion.

i

I

GAS BUBBLE THEORY When product is fluidized by a gas, the frictional force between gas and particles coun-

evaluating alternatives for controlling organic solvent

Documents