EPA-450/3-89-008
CONTROL TECHNOLOGY ASSESSMENT REPORT
FOR AIR EMISSIONS FROM
WASTEWATER TREATMENT OPERATIONS
CONTROL TECHNOLOGY CENTER
SPONSORED BY:
Emission Standards Division
Office of Air Quality Planning and Standards
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Air and Energy Engineering Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Center for Environmental Research Information
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
April 1989
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EPA-450/3-89-008
April 1989
CONTROL TECHNOLOGY ASSESSMENT REPORT
FOR AIR EMISSIONS FROM
WASTEWATER TREATMENT OPERATIONS
by
Scott Harkins and Ashok S. Damle
Research Triangle Institute
P.O. Box 12194
Research Triangle Park, North Carolina 27709
EPA Contracts No. 68-02-4397
Project Officer:
Robert B. Lucas
Emission Standards Division
Office of Air Quality Planning and Standards
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Prepared for:
Control Technology Center
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
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ACKNOWLEDGMENT
This report was prepared for the Control Technology Center by Scott Harkins
and Ashok Damle of Research Triangle Institute. The EPA Project Officer was Robert
B. Lucas of the Office of Air Quality Planning and Standards (OAQPS). Also
participating on the project team were Jim Durham of OAQPS, and Alfred Azevedo
and Carl Beard of the West Virginia Air Pollution Control Commission.
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PREFACE
This investigation of air emissions from wastewater treatment operations was
funded as a project of EPA's Control Technology Center (CTC).
The CTC was established by EPA's Office of Research and Development (ORD)
and Office of Air Quality Planning and Standards (OAQPS) to provide technical
assistance to State and local air pollution control agencies. Three levels of assistance
can be accessed through the CTC. First, a CTC HOTLINE has been established to
provide telephone assistance on matters relating to air pollution control technology.
Second, more in-depth engineering assistance can be provided when appropriate.
Third, the CTC can provide technical guidance through publication of technical
guidance documents, development of personal computer software, and presentation
of workshops on control technology matters.
This investigation was performed at the request of the West Virginia Air
Pollution Control Commission. The report examines air emissions from wastewater
treatment operations at a chemical manufacturing plant. The report presents
information on existing emission controls and options for additional controls, with
associated costs.
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TABLE OF CONTENTS
1.0 INTRODUCTION 1
2.0 PROCESS DESCRIPTION 1
3.0 ESTIMATE OF UNCONTROLLED VOC AIR EMISSIONS 3
4.0 EMISSION REDUCTION MEASURES 6
5.0 EVALUATION OF CONTROL OPTIONS 7
5.1 Refrigeration System Using Glycol 8
5.1.1 Exit Gas Temperature = -5°C 8
5.1.2 Exit Gas Temperature = 2°C 8
5.1.3 Energy Ba lance 10
5.1.4 Cost Estimate for Refrigerated Cooling 13
5.1.4.1 Recovery Credits 14
5.2 Carbon Adsorption System 14
5.2.1 Cost Estimate 15
5.2.1.1 Estimated Capital Costs 15
5.2.1.2 Estimated Operating Costs 16
5.3 Combined Refrigeration and Carbon Adsorption System 16
5.3.1 Cost Estimate ' 17
5.3.1.1 Capital Costs 17
5.3.1.2 Estimated Operating Costs 17
5 .4 Summary 18
6.0 CONCLUSIONS 18
7.0 REFERENCES 20
APPENDIX 21
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LIST OF FIGURES AND TABLES
Figure 1. Simplified Schematic of Sampling Points 2
Table 1. Comparison of Vent Streams Measured by RTI during 9/86
Samp 1 i ng Study 4
Table 2. Determination of Exit Gas Composition and Amount of
Vaoors Condensed (-5°C) 9
Table 3. Determination of Exit Gas Composition and Amount of
Vapors Condensed (2°C) 11
Table 4. Physical Properties 12
Table 5. Comparison of 3 Control Options 19
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1.0 INTRODUCTION
The Occidental Chemical Plant at Belle, West Virginia produces Cj-
chlorinated solvents (e.g., methylene chloride, carbon tetrachloride, and
chloroform). The wastewater generated at this plant is treated in organics/
solids decanters and a steam stripper to recover volatile organics before
discharge. These operations result in substantial air emissions with high
concentration of volatile organics. This report identifies and evaluates
various options available to control the air emissions of volatile organics
(VOCs). The information gathered in field visits by Research Triangle
Institute personnel in September 19861 and July 19882 is usea to estimate the
total annual emissions of the VOCs as well as the maximum rate of emissions
due to working losses from the wastewater treatment operations. Conden-
sation of organics in a refrigeration system, carbon adsorption and a
combination of both techniques are evaluated in this report as possible
control options.
2.0 PROCESS DESCRIPTION
The wastewater at the Occidental Chemical plant consists of equipment
wash water and rainfall collected from diked areas around the plant;-
consequently, the flow rate and composition of the wastewater is cyclical and
dependent upon the amount of rain. Plant personnel indicated in September
19861 that the steam stripper operated roughly 75 percent of the time.
Wastewater accumulates in a storage tank when the stripper is not operating1.
Once the stripper is started, it operates continuously until the wastewater in
storage has been steam stripped.
A flow schematic of the treatment system* is given in Figure 1. (Figure
1 is a simplified block diagram because the more detailed process schematic
was considered to be confidential business information.) The wastewater
enters one of two decanters (each approximately 20,000 gal capacity) where it
is processed as a batch. Sodium hydroxide solution (caustic) is added to the
decanter to adjust the pH and flocculants are added to aid in solids removal.
The mixture is recirculated and mixed in the decanter and allowed to settle.
The wastewater (upper layer) is sent to the stripper feed (or storage) tank
(approximately 125,000 gal capacity). The organic layer (at the bottom) is
removed from the decanter and sent to a surge or collection tank, and solids
are periodically removed and dried in a vacuum dryer. The vapors from the
dryer are collected in a carbon bed adsorber unit.
The steam stripper is started after a sufficient quantity of water has
accumulated in the storage tank. The stripper feed passes through a heat
exchanger for preheating by the effluent from the stripper. The stripper
column is packed with 1-inch saddles and processes about 12 gal/min. The
stripper effluent, after cooling by the heat exchanger, enters one of two
open-topped holding tanks (about 5,000 gal) where it is analyzed for
comparison with the discharge limits. If the analysis is satisfactory, the
water is pumped to a surge tank where the pH is adjusted for final discharge
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i
S9
Vant
Condenser
S1
Water
In
-S12
Vent
Decanter
S3
S2
Sludge
Water
S4
Organics
S10
I
Storage
SB
I
•
Carbon
SB
Vent
Condenser
Decanter
Stripper
Vapors
S6
Water
Water
Holding
Surge Tank
Condensate
-S7
S11
Collection
Tank
Discharge to River
Figure 1. Simplified schematic of sampling points.
(SI, S2, ... S12 indicate sampling locations
during 9/86 sampling study by RTI)
1
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to the river under the NPOES permit. Additional pH adjustments can be made at
the surge tank and final analyses of the water can be performed before
discharge to the river.
The overhead vapors from the stripper pass through a condenser cooled
with cooling tower water. The condensate enters a decanter that separates the
heavier organic layer from water. The entire water layer is returned to the
steam stripper and the organic layer is drained periodically by the operator
to a small collection tank for recycle back to the process. The collection
tank is open-topped and has a layer of water and sludge floating on too of the
organic layer.
The condenser is vented through the decanter to a vent condenser as shown
in Figure 1. The vent condenser is now equipped with a refrigeration system
with glycol coolant available at -10°C. Although equipped, the condenser is
not yet run continuously at the lower operating temperature.2 The vent
condenser receives vapors from the initial water/organics/solids decanters and
the steam stripper condenser/decanter. The initial decanters and storage tank
are fixed roof tanks and have conservation vents that open as necessary to
prevent pressure buildup.
3.0 ESTIMATE OF UNCONTROLLED VOC AIR EMISSIONS
The primary VOC air emission points at the above wastewater treatment
facility are the secondary (vent) condenser outlet and the conservation vents
on decanter and feedwater storage tanks which open whenever liquid is pumped
into these tanks (streams S9, S10, and S12 in Figure 1). The concentration of
the volatile Ci-chlorinated solvents in the various vent emission streams were
measured in the detailed sampling study conducted by RTI in September 1986,*
and are given in Table 1.
The measured concentrations of organics at the outlet from primary and
secondary condensers are very similar in Table 1 because at the time of this
sampling study, the secondary condenser operated at a temperature similar to
that of the primary condenser, resulting in very little additional
condensation. The secondary condenser is now equipped to use refrigerated
glycol as coolant instead of plant cooling water.2 This modification will
allow the condenser to cool the vent gases down to -5°C when fully
operational. For the purpose of estimating uncontrolled emissions, the
measured concentrations (at the secondary condenser outlet as well as at other
vent streams) will be used and the effect of refrigerated glycol cooling will
be considered as one VOC control option.
The vent streams are also nearly saturated with water vapor at the
respective stream temperatures due to the extended contact with the aqueous
phase. Because of the immiscibility of water with the organics phase, the
partial pressure exerted by water vapor will be close to the saturated vapor
pressure. The balance of the vent stream flows is composed of air.
During the September 1986 RTI sampling study,1 typical operating
conditions for the steam stripper and primary condenser were established. The
feed rate to the stripper was about 10.8 gal/min (40.9 1/min) and the
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TABLE 1. COMPOSITION OF VENT STREAMS AS MEASURED BY RTI DURING 9/86 SAMPLING STUDY.
Stream
S8
S9
' S10
Sll
S12
Description
Primary Condenser
Vent
Secondary
Condenser Vent
Storage Tank Vent
Organics
Collection Tank
Vent
Solids Decanter
Vent
CH3C1
0.57
0.53
0.19
0.0051
0.77
Concentration, Mole %
CH2C12
39.18
38.59
11.04
1.81
28.57
CHC13
4.16
4.28
2.86
0.35
7.06
CC14
0.21
0.29
0.76
0.032
2.62
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corresponding average primary condenser vent flow was measured to be about
15.06 gal/min (57 1/min) at standard conditions. The secondary condenser
outlet flow, however, was measured to be about 3.17 gal/min (12 standard
1/min) average. The primary condenser outlet flow rate was measured by
venting the outlet directly to atmosphere. In actual operation, the vapors
leaving the primary condenser travel through long piping to secondary
condenser, causing a significant back pressure (~ 1.5 psig) at the primary
condenser. Also the primary condenser outlet vapors are in direct contact
with the liquid in the collection tank. Thus during flow measurement at the
primary condenser some of the liquid in the collection tank may also have been
flash vaporized causing additional flow. Due to the uncertainties involved in
the primary condenser flow measurement and almost identical comoosition of
primary and secondary condenser outlet streams (indicating almost no
additional condensation in the secondary condenser) the flow rate leaving the
primary condenser is assumed to be the same as measured flow at the secondary
condenser; i.e., 3.17 gal/min (12 1/min) for a steam stripper feed rate of
10.8 gpm (40.9 1/min).
Attempts to measure the vent flows from the decanter tank and storage
tank with the liquid pumping into the tanks failed during the previous
sampling study because of opening of conservation vents. The conservation
vents are designed to keep the headspace pressure in the tanks within 0.188 -
0.25 psi of atmospheric pressure. Thus the rapid filling of liquid, as
currently practiced, forces the conservation vents to open releasing tne
vapors to atmosphere. The vent flows from these tanks may simply be assumed
to be equal to liquid feed rate because of volumetric displacement of the gas
with incoming liquid. The total amount and rate of tank vent gases displaced
is thus equal to the total volume and rate of the liquid feed in the decanter
and storage tanks.
The relatively low vapor phase concentration at Sll and low working
losses from the low rate of condensate generation suggest that the air
emissions from the organics collection tank would be much lower than the other
sources; e.g., for the 10.8 gpm stripper feed rate the rate of primary
condensate is about 0.08 gal/min (0.3 1/min), as compared to 3.17 gal/min (12
1/min) primary condenser vent flow rate. Furthermore, the concentration of
organics in the collection tank headspace is 2.2% as compared to 44.1% in the
condenser outlet vapors. Thus, VOC emissions from Sll may be expected to be
only about 0.1% of the primary condenser outlet emissions. Therefore, these
emissions will be ignored in the present study.
Recent inquiries with Occidental Chemical Plant personnel^ indicated that
the total amount of the wastewater processed average to about 6.5 gpm for
24 hrs/day, 365 days/yr operation. Thus the total amount of wastewater
processed in one year = 3.4164 x 106 gallons (-12.93 x 106 liters). Since the
total amount of wastewater is fed into decanter tanks and subsequently to
feedwater storage tank and then to steam stripper, the total amount of vent
flows from each of the major sources may be estimated for the above given
total annual wastewater flow. The individual organic compound annual
emissions may be determined using their measured concentration given in
Table 1:
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1) Decanter Tank Vent, S12: 12.93 x 105 liters/year & 25°C
Methyl Chloride
Methylene Chloride
Chloroform
Carbon Tetrachloride
Total
2.056 x 105 gm/yr
1.284 x 107 gm/yr
4.462 x 106 gm/yr
- x
452.9 Ib/yr
2.829 x 104 Ib/yr
9.827 x 103 Ib/yr
-l-J-QO x 103_Ib/yr
1.964 x 107 g»/yr ~ 4.326 x 104 Ib/yr
2) Storage Tank Vent, S10:
Methyl Chloride
Methylene Chloride
Chloroform
Carbon Tetrachloride
Total
12.93 x 106 liters/year & 25°C
~ 5.074 x 104 gm/yr ~ 111.77 Ib/yr
~ 4.963 x 106 gm/yr ~ 1.093 x 104 Ib/yr
~ 1.807 x 106 gm/yr ~ 3.981 x 103 Ib/yr
- 6.189 x 105 gm/vr -1.363^_LQ?_1 b/yr
7.440 x 106 gB/yr - 1.639 x 104 Ib/yr
3) Primary Condenser
Outlet Stream, S8:
Methyl- Chloride
Methylene Chloride
Chloroform
Carbon Tetrachloride
Total
3.796 x 106 liters/year @ 0°C
4.878 x 104 gm/yr
5.644 x 106 gm/yr
8.424 x 105 gm/yr
5.480 x 104 qm/vr
107.45 Ib/yr
1.243 x 104 Ib/yr
1.856 x 103 Ib/yr
120.7 Jb/yr
6.590 x 106 g»/yr - 1.452 x 104 Ib/yr
The total uncontrolled VOC emissions from all 3 sources is thus
calculated to be about 33.67 Mg/yr, 74,163 Ibs/yr.
Another important aspect from control standpoint is the rate of
emissions. The rate of primary condenser outlet vapors is 12 standard 1/min
when the stripper is in operation, which would roughly be 60% of the time
given the normal stripper feed rate and average wastewater generation rate.
In the September 1986 study, the stripper operation time was estimated to be
about 75$ of the time1. The reduction from 75% to 60% may be perhaps because
of reduced wastewater generation rate due to recent plant modifications.
Since the stream concentration used in estimation were the same as those used
in the September 1986 study, the reduced wastewater generation rate resulted
in a lower estimate of 33.7 Mg/yr VOC emissions as compared to 44 Mg/yr
estimate1 in the previous sampling study report. The normal pumoing rates as
provided by plant personnel during RTI's recent visit^ are: 48 gpm for
wastewater feed into decanters and 120-140 gpm for liquid feed from decanters
to feedwater tank. Thus liquid feed operation into decanters is carried out
over only 13.5% of total time and the liquid pumping into feedwater tank
occurs only 5% of the time.
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4.0 EMISSION REDUCTION MEASURES
The emissions from the feedwater storage tank result when liquid is
pumped from the decanter tank to the feedwater tank. Due to the high rate of
liquid pumping the conservation vent opens letting out the emissions. At
present the feedwater tank headspace is not connected to the decanter tank
headspace. The vapor emissions from feedwater tank may be prevented by simply
connecting the feedwater tank headspace to the decanter tank head space by a
duct. This will allow the displaced vapors to enter the decanter tank during
liquid pumping operation. The duct should be of large enough size to handle
130 gpm or 17.4 ft3/min (492.1 1/min) flow rate with minimal pressure drop «5
inches of water ~ 0.2 psi) to prevent opening of the conservation vent. This
simple ducting arrangement will eliminate 7.44 Mg/yr (16,402 Ibs/yr) VOC
emissions from the feedwater storage tank, and the total VOC load on a control
system- will be reduced to 26.23 Mg/yr or 57,753 Ibs/yr. Recent discussion
with plant personnel2 indicated that this duct installation will cost UD to
$3,000 including materials and labor.
In order for any control system to be effective all the vent emission
must pass through the control system. Thus a forced drive system downstream
of a control system is essential to prevent opening of conservation vents on
the decanter and feedwater tanks. The fan or blower must automatically be
turned on whenever any liquid pumping operation starts or the steam striooer
is running. The vent flow rate from primary condenser is typically 12 stan-
dard 1/min, which will be present 60% of the time. The maximum flow rate that
the drive system would need to be able to handle is 12 standard 1/min + 182
lit/min (48 gal/min) from the decanter tank or about 194 1/min (7 ACFM) total.
Thus the fan must be able to deliver 7 ACFM of maximum flow in order to
prevent pressure buildup in the decanter and feedwater tanks during liauid
filling operations and consequently to prevent opening of conservation vents.
The fan should also be able to reduce the flow to 12 1/min when only the steam
stripper is in operation to prevent excessive vacuum in the decanter and
feedwater tanks. Due to the variability of the total vent emission'flow rate.
the fan should be of flexible capacity from 10 to 200 1/min (0.3 to 7.5 ACFM)
and its operating caoacity should be controlled by the wastewater treatment
operation.
Also it is very important to prevent any unwarranted emissions such as
those occuring through overflow vents for liquid level. During RTI's earlier
sampling trip,1 it was found that vapors from the decanter tanks were
discharging at ground level through pipes installed as overflow lines
connected near the top of the tanks. These lines were plugged for RTI's
sampling and were reported to plant personnel for modification such as
installation of traps on decanter tank overflow plumbing. No vent control
system will operate properly when vent gases discharge through uncontrolled
exits. This problem was reidentified to current plant personnel during RTI's
most recent sampling trip2, for proper modifications.
5.0 EVALUATION OF CONTROL OPTIONS
The emission of volatile organics from the steam stripper plant may De
reduced by condensing the organics at a lower temperature or by using a carbon
adsorption system. A combination of both approaches is also possible. The
secondary vent condenser at Occidental's wastewater treatment plant is now
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equipped to use refrigerated glycol at -5 to -10°C as coolant. This lower
operating temperature as compared to primary condenser would allow additional
organics to condense thereby reducing their emissions. Carbon adsorption
systems have been shown to be very effective for removing chlorinated
organics.3 The Occidental plant uses such a carbon adsorption system to treat
sludge dryer emissions. The dryer vapor emissions are thus reported to be
reduced by more than 99%.2
5.1 Refrigeratjon_System Using Jjlycqj
5.1.1 Exit Gas Temperature = -5°C
The refrigerated glycol is available at -5 to -10°C. Thus it may be
assumed that the vent gases can be cooled only down to -5°C. Because of the
intermittent nature of the two primary emission sources and difference in the
stream compositions, the condenser performance can change with time. Looking
at the estimate of total emissions, almost 75% of the total VOC emissions come
from decanter tank vent. The maximum load that the condenser will experience
may be determined by assuming that the liquid is pumped into the decanters
while the steam stripper operates. The total maximum vent flow rate at such
conditions would be ~ 194 1/min with a comoosite composition of S8 and S12
stream as follows:
CH3C1 0.76 mol%
CH2C12 29.23 mol%
CHC13 6.88 mol% •
CC14 2.47 mol%
Inerts + Water 60.66 mol%
The stream may also be assumed to be saturated with water vaoor at the
primary condenser exit temperature of 21°C. Since water is immiscible with
organics phase, its concentration in the vent gases would be 2.45 mol%.
corresponding to the saturated vapor pressure.
For the above feed composition and for condenser exit vapor temperature
of -5°C. the amount of vapor that would be condensed may be calculated from
equilibrium considerations as shown in Table 2. The calculations take into
account the immiscibi1ity of the water and organic phases and uses Raoult's
law to calculate equilibrium vapor pressure of each organic component. The
computation for vapor exit temperature of -5°C indicate that almost 11.1% of
the organic vapors may be condensed in the secondary condenser.
Applying individual condensation efficiencies for each component total
organic vapor emissions after condensation may be estimated:
Methyl Chloride ~ 2.099 x 105 gm/yr ~ 462.3 Ib/yr
Methylene Chloride ~ 4.542 x 106 gm/yr ~ 10,000 Ib/yr
Chloroform ~ 6.217 x 105 gm/yr ~ 1,369 Ib/yr
Carbon Tetrachloride ~ 1.499 x 105 qm/yr ~ 330.2 Ib/yr
Total VOC Emissions 5.524 Mg/yr ~ 12,166 Ib/yr
In terms of VOC mass emission, the secondary condenser operated at gas
exit temperature of -5°C would reduce mass emission by 78.9% to 5.52 Mg/yr.
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TABLE 2. DETERMINATION OF EXIT GAS COMPOSITION AND AMOUNT OF VAPORS CONDENSED.
Basis: 1 gmole of Feed Vapor
Exit Gas Temperature = -5°C
Feed Gas
Component
CH3C1
CH2C12
CHC13
CC14
— — - •
H20
Inert
•• •
Moles in
Feed Gas
0.0076
0.2923
0.0688
0.0247
• • ...
0.0245
0.5821
% of Feed
Condensed
17.49
75.43
88.28
93.15
Moles
Condensed
0.001329
0.2205
0.06074
0.0230
0.30556
ni
Moles
in Gas
0.00627
0.07182
0.00806
0.00169
0.0028
0.5821
0.67274
XT
Organic Phase
Mole Function
0.004350
0.721576
0.198774
0.075299
Ki
Relative
Volatility
2.1434
0.14792
0.06030
0.03339
Mi
Equilibrium Gas
Phase Mole Fraction
0.009324
0.106735
0.011986
0.002514
YI = Hi/En,
Gas Phase Mol
Fraction
0.009321
0.106753
0.011985
0.002514
0.004162
0.865265
1.0
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5.1.2 Exit Gas Temperature = 2°C
Because of the intermittent nature of emissions one potential problem in
keeping condenser exit gas temperature below 0°C is icing. Whenever vapor
flow to condenser stops, ambient humidity can easily enter the condenser and
cause icing blockage problems. One way to prevent icing is to keep the exit
gas temperature above 0°C. Therefore, condensation eauilibrium calculation
were also carried out for exit gas temperature of 2°C, as shown in Table 3.
Because of the higher exit gas temperature, the condensation of orqanics would
be decreased to about 67.4%. By applying individual condensation efficiencies
for each component, the total organic vapor emissions after condensation at
2°C may be estimated:
Methyl Chloride
Methylene Chloride
Chloroform
Carbon Tetrachloride
Total VOC Emissions
- 2.241 x 105 gm/yr ~ 493.7 Ib/yr
~ 6.669 x 106 gm/yr ~ 14.696 Ib/yr
~ 1.012 x 106 gm/yr ~ 2,229 Ib/yr
- 2.559 x 105 qm/yr ~_56.3..6L JJp/yr
8.161 Mg/yr ~ 17,976 Ib/yr
The reduction in VOC mass emission in this case would be 68.9%, with
emissions of 8.16 Mg/yr.
5.1.3 Energy Balance
The existing secondary vent condenser consists of eight (8) 3/4" ID and
10' long tubes. In order to determine the ability of this condenser to handle
all of the vent vapor emissions load, an energy balance was carried out.
Since the gas cooling to -5°C involves maximum condenser duty with minimum
temperature driving force, the exit gas temperature was assumed to be -5°C in
energy balance calculations.
Basis (mass balance): 1 gmole of feed gas to condenser @ 25°C
Basis (energy balance): Enthalpy of liquid phase = 0 @ -5°C
Assume that gases are cooled down to -5°C at exit. The physical properties of
each component in the gas phase are given in Table 4. The mole fraction of
each component in the feed and exit gases as well as moles of liquid condensed
are given in Table 2.
Enthalpy of condensate liquid out = 0
Enthalpy of exit gases (as given by latent heat):
CH3C1
CH2C12
CHC13
CC14
H20
Air
0.00627 x 4934.36
0.071818 x 7232.12
0.008063 x 7791.77
0.001691 x 8070.58
0.0028 x 10991.48
Latent heat ignored
Total Enthalpy of Exit Gases
30.94 cal
519.40 cal
62.83 cal
13.65 cal
30.78 cal
_Q
= 657.60 cal
10
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TABLE 3. DETERMINATION OF EXIT GAS COMPOSITION AND AMOUNT OF VAPORS CONDENSED.
Basis: 1 gmole of Feed Vapor
Exit Gas Temperature = 2°C
Feed Gas
Component
CH3C1
CH2C12
CHC13
CC14
H20
Inert
Moles in
Feed Gas
0.0076
0.2923
0.0688
0.0247
0.0245
0.5821
% of Feed
Condensed
11.89
63.92
80.92
88.31
Moles
Condensed
0.000903
0.186838
0.055672
0.021812
0.265227
ni
Moles
in Gas
0.00669
0.10546
0.01313
0.00289
0.0050
0.5821
0.71527
*1
Organic Phase
Mole Function
0.003407
0.704445
0.209906
0.082241
Ki
Relative
Volatility
2.7486
0.2093
0.08742
0.04912
KiXi
Equilibrium Gas
Phase Mole Fraction
0.009364
0.14744
0.01835
0.004039
Yi = ni/Eni
Gas Phase Mol
Fraction
0.009361
0.147442
0.018352
0.004036
0.00699
0.81382
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TABLE 4. PHYSICAL PROPERTIES
r\>
Component
CH3C1
CH2C12
CHC13
CC14
H20
Air
Heat of
Vaporization
(? -5»C
cal/gmole
4934.36
7232.12
7791.77
8070.58
10,991.48
—
Gas Phase
Specific Heat
(-5° to 25°C)
cal/gmole °K
9.44
11.81
15.37
19.71
8.014
6.902
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Enthalpy of gases entering condenser (as given by latent and sensible
:
heat)
CH3C1
CH2C12
CHC13
CC1
H20
Air
4
0.0076 x (4934.36 + 9.44 x 30) = 39.65 cal
0.2923 x (7232.12 + 11.81 x 30) = 2217.51 cal
0.0688 x (7791.77 + 15.37 x 30) = 567.80 cal
0.0247 x (8070.58 + 19.71 x 30) = 213.95 cal
0.0245 x (10991.48 + 8.014 x 30) = 275.18 cal
0.5821 x (6.902 x 30) = _12CL_53_ca1
Total Enthalpy of Feed Gas = 3434.62 cal
Therefore, energy removed in the condenser = 2777 cal/gmole feed gas.
Maximum flow rate of feed gas = 194 1/min @ 25°C =7.93 gmoles/min.
Thus maximum condenser heat duty = 7.93 x 2777.02
= 2.202 x 104 cal/min
= 87.39 Btu/min
=0.44 ton of refrigeration
Existina secondary condenser inside surface area = rr x (0.75/12) x 8 x 10
= 15.71 ft2
Assuming glycol temperature of -6°C on cooling liquid side, the log mean
temperature gradient = 8.74°C. Therefore, to achieve, the maximum required
condenser duty the overall heat transfer coefficient required
= 87.39 x 60 / (15.71 x 8.74 x 1.8)
= 21.2 Btu/hr-ft2-°F
Since the typical value for overall heat transfer coefficient for
condensers is usually between 40 - 100 Btu/hr-ft2-°F. the existing condenser
may be expected to satisfactorily handle the maximum condensation load.
5.1.4 Cost Estimate for Refrigerated Cooling
Since the secondary condenser is already in place and equipped for glycol
cooling, no additional capital cost is reauired. The maximum heat duty
required is only 0.44 tons of refrigeration. According to the plant
personnel2 10-15 tons of refrigeration capacity is currently available at the
plant site with an operating cost of $1000/ton/year.
Thus the operating costs associated with glycol cooling would be less
than $500/year. In addition, operator/maintenance labor cost may be
considered as ~ $1.825/yr, @ 0.5 hr/day and $10/hr. The total operating costs
may thus be calculated to be about $2,325/yr.
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5.1.4.1 Recovery Criggjts
With a condenser operating temperature of -5°C almost 45,580 Ibs of
organics will be recovered per year. The corresponding recovery credit will
be $5,700/yr @ $0.125/lb of organics recovered.
For higher condenser operating temperature of 2°C about 39.780 1b of
organics will be recovered resulting in $4,970 recovery credit @ $0.125/lb of
organics recovered.
5-2 Carbon Adsorption System
Since the maximum expected vent flow rate is only 194 1/min (~ 7 ft3/min)
the design of carbon adsorption system will simply be based on the desired
capacity. The activated carbon may generally be expected to be very efficient
for higher chlorinated hydrocarbons.3 The adsorption capacity of activated
carbon for methyl chloride under dry conditions is about 0.03 lb/ Ib carbon.
whereas for methylene chloride, chloroform and carbon tetrachloride the
capacity under dry conditions is about 0.5 Ib/lb carbon according to one
vendor.3 The low capacity for methyl chloride will not be a significant
problem in the present case due to its low gas phase concentration compared to
methylene chloride. For humid saturated conditions the dry capacities may be
reduced3 by 60 - 70%, i.e.. the reduced capacity would be 0.02 Ib/lb carbon
for methyl chloride and 0.35 Ib/lb carbon for the other organics. The removal
efficiency for all organics is expected to be greater than 99% for inlet vapor
concentrations in the percentage ranges. Methyl chloride is likely to be the
first compound to break through due to its low capacity for adsorption.
For a system employing parallel beds with alternate adsorption and steam
regeneration, the working caoacity may be expected to be reduced as compared
to fresh carbon capacity. Due to the low boiling compounds, the working
capacity is likely to be reduced by only 5% according to one vendor.3 For a
conservative estimate, a 50% reduction in the capacity will be assumed in the
present case. Thus the capacity of carbon under water saturated conditions
may be considered to be 0.01 Ib/lb carbon for methyl chloride and 0.17 Ib/lb
carbon for other organics.
The total emission of uncontrolled organics as estimated in sections 3.0
and 4.0 is about 57,800 Ib/year or about 158.4 Ib/day. For a one-day
adsorption/regeneration cycle, the amount of carbon required in the adsorption
bed using capacity for higher hydrocarbons is 932 Ibs. Due to low concen-
tration of methyl chloride, this amount of carbon will have an adequate
capacity to adsorb all of methyl chloride as well.
For design consideration, two parallel beds holding 1000 Ib of activated
carbon each may be assumed. With a typical carbon bulk density3-4 of about 30
lb/ft3, the volume of the carbon bed is calculated to be 33.33 ft3. A 3.5'
dia, 6.5' tall vessel with an internal volume of 62.8 ft3 will be adequate to
house 1000 Ibs of carbon. Steam stripping of an exhausted bed followed by
condensation may be expected to recover almost 90% of the organics. The vent
stream flow from the adsorber/condenser may be added into the total vent
stream of the wastewater treatment plant to be processed again. Condensate
liquid may be decanted into organic and aqueous fractions. The organic
14
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fraction may be recycled to the process along with the organic condensate from
primary and secondary condensers. The aqueous stream can be sent back to the
wastewater treatment system, making all streams integrated to the existing
wastewater treatment plant.
With a 99+% removal efficiency in the adsorber the organic emissions will
be reduced to 580 Ib/year or less. Since the wastewater treatment system is
of intermittent nature, the carbon adsorption beds must be equipped with a VOC
detector at the outlet to signal breakthrough and need for regeneration.
5.2.1 Cost Estimate
5.2.1.1 Estimated ._CajDitaljCp.sts
The capital and operating costs associated with the carbon adsorption
system may be estimated using the guidelines provided in the EA8 Control Cost
Manual.5
Initial Carbon, 2000 Ibs $ 4,000
@ $2/lb of fresh carbon
2 Adsorber Vessels 15,000
(3.5' diameter, 6.5' tall)
Fan, pumps, decanter,
condenser, internal piping LAQO
[0.39 (4,000 + 15,000)]
Adsorber equipment total cost $26,400
Instrumentation, taxes,
freight, (0.18 x 26,400) ._j*..750
Total purchased equipment $31,150
Installation Cost (-30%)
(foundation, supports,
erection, electrical,
piping, insulation, etc.) 9,350
Indirect cost (-31%)
(engineering, supervision,
construction and field expenses,
construction fee, startup, etc.) 9,650
Cost of ductwork^ to bring vent
gases from secondary vent condenser
outlet to adsorber system (including
installation) 5jpOO
Total Capital Investment $55,150
15
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5.2.1.2
jOBerat_irrg .Costs
i) Steam Cost: steam consumption @ 3.5 Ib/lb adsorbed VOC
~ 2.023 x 105 Ib/yr
Steam cost @ $5/1000 Ib
ii) Cooling water cost:
(same as steam cost)
iii) Electricity
(very little pressure drop
across bed due to low flow)
$l,000/yr
1.000/yr
200/yr
1,200/yr
7,420
3,650/yr
$14,470
$ 6.500/yr
iv) Carbon replacement
(for 5-year carbon life)
0.2638 (1.08 x 4000) + 250
v) Indirect annual cost
[50,150 - (1.08 x 4000 +250)] x 0.1628
vi) Operating and maintenance labor
(1 hr/day @ $10/hr)
Total Annual Operating Costs
Possible Recovery credit
(with a 90% recovery, rate about 52,020 Ib
of organics will be recovered every year
resulting in $6500 recovery credit
@ $0.125/lb) of recovered organics)
5.3 Cpmbined JRefrj^ej.atJon_and_Caf^ojn__Adsprp_tjort.System
In this option, a carbon adsorption system will be installed downstream
of the secondary vent condenser to take advantage of the existing secondary
condenser facility and to reduce load on the carbon adsorption system.
Because of the icing problems associated with lower operating temperature of
-5°C, the condenser is assumed to operate at a temperature of 2°C. From
section 5.1.2, the resultant organic loading on the carbon adsorption system
would be about 18,000 Ib/year, or about 49.3 Ib/day.
The secondary condenser also will reduce the amount of water vaoor in the
gas stream considerably increasing the adsorption capacity of the activated
carbon. Assuming a conservative 50% reduction in the carbon capacity due to
regeneration, the capacity of the activated carbon may be assumed to be 0.25
Ib/lb carbon. The amount of carbon required for one day cycle is therefore
about 200 Ib/day. The corresponding volume of carbon would be 6.67 ft3. A
vessel of 2' diameter and 4' depth with an internal volume of 12.6 ft3 will be
able to house 200 Ibs of activated carbon.
Due to low concentration of methyl chloride, this amount of carbon will
have an adequate capacity for adsorbing all of the methyl chloride as well.
16
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With 99+% removal efficiency for organics, their emission may be expected to
be reduced to 180 Ib/year or less. Again, due to the intermittent nature of
the wastewater treatment system, the carbon adsorption beds must be equipped
with a VOC sensor at the outlet to signal VOC breakthrough and need for
regeneration.
Because of the intermittent nature of the wastewater treatment system, it
may also be possible to use a single larger bed of carbon and regenerate it
every 4 to 5 days whenever steam stripper and liauid filling operation are not
in progress. For example, a single bed of 1000 Ib carbon as discussed in
section 5.2 will be able to provide enough carbon for 5 days. However, an
adsorption system with two smaller beds may be preferable as it will not out
any constraints on the main wastewater treatment plant.
5.3.1 Cost Estimate
A two-bed system with each holding 200 Ib of carbon is considered for
cost estimation. The capital and operating costs are based on the EAB Control
Cost Manual guidelines.5
5.3.1.1
ital Costs
Capital costs may be determined using rule of scale and the cost of the
larger system discussed in 5.2. Using a scaling factor6 of 0.6, the capital
cost for the adsorption system may be estimated to be:
- $50,150 (l/5)0-6 ~ $19,100
Cost of ductwork2 to bring vent 5,000
gases from secondary vent condenser
outlet to adsorber system (including
installation)
Total Capital Investment $24.100
5.3.1.2 Estimated Operating Costs
i) Steam cost: (? 3.5 Ib/lb of adsorbed VOC $ 340/yr
and $5/1000 Ib steam
ii) Cooling water cost 340/yr
iii) Electricity 200/yr
iv) Carbon replacement for 5-year 300/yr
carbon life: 0.268 (1.08 x 800 + 250)
v) Indirect annual cost for carbon 2,930/yr
adsorption system
[19,100 - (1.08 x 800 + 250)] x 0.1628
vi) Glycol refrigeration cost (section 5.1.4) 500/yr
17
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vii) Operating and maintenance labor 5,474/yr
(1.0 hr/day @ $10/hr) - Adsorption sys.
(0.5 hr/day @ $10/hr) - Refrigeration sys.
Total Operating Costs $10,085/yr
Possible Recovery Credit:
Secondary Condenser System (sec. 5.1.4.1) 4,970/yr
Adsorption System 2,030/yr
(With a 90% recovery rate, about 16,200 Ibs
of organics will be recovered every year
by the adsorption system resulting in
$2,025 credit 9 $0.125/lb
Total Recovery Credit $7,000/yr
5.4 Summary
The estimates for cost, emission of organics and recovery of organics for
each option are summarized in Table 5. Due to the limited time available for
this study, no optimization of the control systems is made, e.g. adsorption
cycle time. The costs presented are therefore rough estimates for preliminary
assessment. As seen from this table, use of secondary vent condenser with
refrigerated glycol cooling followed by carbon adsorption offers the lowest
cost for high organics removal efficiency. The refrigerated cooling alone
provides the best ratio of organics removed per total cost, however, it will
still result in significant organic emissions of 12,000 to 18,000 Ibs/year.
6.0 CONCLUSIONS
Based upon this study, the following conclusions may be drawn for
efficient organics removal from wastewater treatment system vent VOC emissions
at the Occidental Chemical Plant at Belle, West Virginia.
1. Connecting the headspaces of storage feedwater tank and decanter
tanks will eliminate the source of VOC vent emissions (working
losses) at the feedwater tank. This will result in 7.44 Mg/yr
reduction in VOC emissions.
2. For any control system to be effective, a forced drive system such as
a fan or blower at the downstream of the control system is essential
to carry the vent gases through the system and to prevent opening of
the conservation vents. Moreover, the fan should be of flexible
capacity controlled by wastewater treatment operations. For example,
whenever liquid is being filled in the decanter tank, the fan must
pull vent streams at the same rate as liquid pumping rate; and when
only the steam stripper is running the fan must reduce the vent flow
rate accordingly so as not to cause any vacuum in the storage or
decanter tanks.
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TABLE 5. COMPARISON OF THREE CONTROL OPTIONS.
Option f
1
1A
2
3
Description
Refrigerated
cooling at -5°C*
Refrigerated
cooling at 2°C
Carbon adsorption
alone
Refrigerated
cooling at 2°C
followed by
carbon adsorption
Amount of
Organ ics Removed
(Ibs/yr)
45.590
39,750
57,170
57,570
VOC Emissions
( Ibs/yr)
12,160
17,980
580
180
Total
Capital
Cost, $
—
—
55,150
24,100
Annual
Operating
Costs, $/yr
2.325
2,325
14.470
10.090
Possible
Recovery
Credit, $/yr
5.700
4,970
6.500
7,000
Possibility of icing blockage problems
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3. It is necessary to prevent any unwarranted vapor emissions such as
those occurring through overflow vents for liquid level (e.g.,
decanter tank overflow plumbing) by installing liquid traps.
4. The secondary vent condenser is capable of condensing up to 68% by
mass of vapors in the feed stream using refrigerated glycol cooling
operated at the gas exit temperature of 2°C. This will result in
recovery of 18.07 Mg/yr of organics with annual VOC emissions of 8.16
Mg/yr.
5. A combination of the refrigerated glycol cooled secondary condenser
and a subsequent carbon adsorption system will be able to remove
almost all of the organics in the vent emissions at a lower cost than
that for a carbon adsorption system alone. The value of recovered
organics will be able to pay for almost 70% of the total operating
costs. The VOC emissions may be expected to be reduced to 180
Ibs/yr.
7.0 REFERENCES
1. Branscome, M., S. Harkins, and K. Leese, "Field Test and Evaluation of
the Steam-Stripping Process at Occidental Chemical, Belle, WV", Research
Triangle Institute Project Report prepared for Hazardous Waste
Engineering Research Laboratory, U.S. EPA Contract No. 68-03-3253, Work
Assignment 1-6, March 1987.
2.- Harkins, S. Report to EPA/OAQPS of trip to Occidental Chemical Plant,
Belle, WV, September 1988. (Attached as an Appendix to this report).
3. Roy, Al, Calgon Corporation, Technical Representative, personal
communication. August 1988.
4. Spivey, J.J., "Recovery of Volatile Organics from Small Industrial
Sources", Environmental Progress, Vol. 7, No. 1, pp. 31-40, February
1988.
5. Vatavuk, W.M., W.L. Klotz and R.L. Stallings, "Carbon Adsorbers" Section
4 in EAB Control Cost Manual, 3rd ed., EPA 450/5-87-001A, February 1987.
6. Peters, M.S. and K.D. Timmerhaus, "Plant Design and Economics for
Chemical Engineers", pp. 166-167, McGraw-Hill Bank Company, New York,
1980.
20
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APPENDIX
Report for RTI Trip to Occidental Chemical Plant,
Belle, WV. July 1988
21
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RESEARCH TRIANGLE INSTITUTE
Center for Process Research James J. Spivey, Ph.D
Director
September 12. 1988
MEMORANDUM
TO: Robert B. Lucas, EPA/OAQPS
FROM: Scott Harkins. RTI
RE: Report for the Trip to Occidental Chemical Plant. Belle. WV
Purpose
The purpose of this trip was to discuss organic vapor emissions from
Occidental's steam stripper and wastewater treatment operations, source of the
emissions, and possible control options; and to obtain additional information.
Place
Occidental Chemical Corporation
Electrochemicals Division
Belle Plant
P. 0. Box 615
Belle, WV 25015
Attendees
Scott Harkins. RTI
Robert Lucas, EPA-OAQPS
Al Azevedo. West Virginia APCC
Larry Hearn, Occidental
Steve Meadows, Occidental
Post Office Box 12194 Research Triangle Park, North Carolina 27709 Telephone: 919 541 -6000
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S. Harkins Trip Report to Lucas '
On July 1. 1988 Scott Harkins (RTI) and Bob Lucas (EPA/OAQPS) conducted a
site visit to the West Virginia Air Pollution Control Commission and the
Occidental Chemical Corporation's Plant in Belle W.Va. This visit was to
discuss organic vapor emissions from Occidental's steam stripper and
wastewater treatment operations, the generation of the emissions, and possible
control options. Additional process information was requested to assist in
evaluating vapor emissions control options.
Bob Lucas and Scott Harkins initially met with Al Azevedo (West Virginia
Air Pollution Control Commission (APCC). 1158 Washington St. East, Charleston,
W.Va.. 25311. (304) 348-4022) for an hour before proceeding to the Occidental
plant. At the Occidental plant Lucas, Harkins, and Azevedo met with Larry
Hum and Steve Meadows (Occidental Chemical Corporation, Electrochemicals
Division. Belle Plant, POB 615, Belle, W.Va.. 25015, (304) 949-4515). Larry
Hum was the principal contact at the plant. The steam stripper equipment was
examined after a discussion (approx. 1 hr) with the plant personnel. Lucas,
Harkins, and Azevedo ate lunch after leaving the plant. This was followed by
a short meeting at the W.Va APCC offices prior to departure.
Al Azevedo related the APCC's recent involvement with the plant. The
W.Va. APCC conducted a risk assessment of air pollutants in the Kanawa valley
from the chemical plants in the region. Although the Belle Occidental plant
is a relatively small chemical plant the risk assessment indicated its
emissions were the most significant risk in the area. The largest source of
emissions from the plant was fugitive emissions while the second highest was
from the wastewater processing operations. The plant has hired a contractor
to check for leaks on a quarterly basis. The discovered leaks are then
repaired to reduce fugitive emissions. W.Va. APCC would like the Control
Technology Center (CTC) of EPA/OAQPS to assess possible control technology
options to minimize emissions of volatile organic chemicals (VOC) from the
wastewater treatment facility at Occidental Chemical.
RTI sampled the steam stripper process and vents in September 1986 as part
of an EAA-ORD project. The vent emission measurements and estimates of total
emissions were used by WVAPCC in the risk assessment for the plant. The vapor
emissions reported by RTI were much higher than earlier estimates of vapor
emissions from the wastewater treatment system (estimated as 79 Ibs of organic
vapor/year in the 1984 inventory of the plant site). The organic vapor
concentrations in gas above water in the decanter tanks and feedwater tank
were much higher than previously believed. The ineffectiveness of the
condenser for the decanter tanks (secondary steam stripper condenser) was not
identified prior to RTI's sampling of the wastewater treatment process.
Several changes to the wastewater treatment system have occurred since
RTI's 9/86 sampling of this process:
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S. Harkins Trip Report to Lucas
Page 2
1) A sludge drier is currently being installed for the dehydration of
decanter tank sludge. This drier is adjacent to the decanter tanks and
feed sludge is pumped directly into the drier. The drier operates under
a vacuum and two sets of condensers/decanters are placed before and after
the vacuum pumps. Gases from the second condenser/decanter (glycol
cooled) are passed through two carbon beds (in series) prior to
discharge. Used carbon beds will be collected by the activated carbon
vendor/supplier and regenerated offsite. The sludge dewatering system
(when operated properly) would not significantly increase the vapor
emissions from the treatment operations due to the carbon bed VOC control
system installed.
2) Another significant change to the system was the conversion of the
decanter tank condenser from plant cooling water to refrigerated glycol
The operating temperature of the condenser will be -6 to -8 °C when
operational. This will condense much more of the vent gas from the
primary steam stripper condenser. It is connected to but will not
efficiently condense the vent flows from the decanter tanks during tank
filling, as these flows are too high for the condenser and the decanter
tank conservation vents will open and vent to the atmosphere.
3) One modification which should have occurred was the installation of
traps on decanter tank overflow plumbing. During RTI's earlier sampling
trip we found that vapors from the decanter tanks were discharging at
ground level through pipes installed as overflow lines connected near the
top of the tanks. These lines were plugged for RTI's sampling and were
reported to plant personnel for modification. No vent control system
will operate properly when vent gases discharge through uncontrolled
exits. This problem was reindentified to current plant personnel for
proper modification.
4) Several modifications to the plant operating conditions have reduced
the volume of wastewater for treatment. Heat exchangers at several
locations were changed from steel to titanium. The new heat exchangers
require cleaning less frequently and produce less wastewater from the
cleaning operations. New gutters were installed on a plant building
routing rainwater to rainwater discharge rather than the wastewater
treatment plant. Feed filtering systems for the distillation columns
were improved, increasing intervals between cleanings. These changes
result in less operation of the wastewater treatment system. Although
the above mentioned changes may reduce the total amount and rate of
wastewater generation, it may not necessarily reduce the organic vapor
concentration in various vent streams as measured in RTI's September 1986
sampling study. Also, since the maximum vent flow rates are determined
by liquid pumping rate into the decanter and feedwater tanks and by
operating rate of the steam stripper, these flow rates will not be
affected by these plant modifications.
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S. Harkins Trip Report to Lucas »
Page 3
There are no current standards for the vent emissions and the control
design should remove a large percentage of the methyl chloride (Ch^Cl),
methylene chloride (Q^C^) chloroform (CHCla), and carbon tetrachloride
(CC14). The vent emissions predominantly contain methylene chloride and
chloroform and thus the control strategy should focus on these to compounds.
The measurements of vent concentrations and flowrates collected by RTI in
1986 will be used for the control design and calculations of vent emission
rates. There are no additional data collected since the last study on the
process vent streams to be included in the design. These data were collected
in the month of September but will be assumed to be representative of the
plant vapor emissions during the entire year.
Additional information provided by Larry Hum of Occidental Chemical Plant
regarding wastewater treatment system operation is given below":
1. Refrigerated glycol temperature cooling
2. Refrigerated glycol availability at
the plant
3. Glycol operating costs at the plant
4. Steam cost at the plant
5. Carbon used in the adsorption system
on sludge dryer emissions
6. Carbon cost (fresh)
7. Offsite carbon regeneration cost
8. Recent changes to steam stripper operation
9. Size of the secondary vent condenser
10. Current average rate of wastewater
treatment
11. Flow rate into decanter tanks
-5*C minimum
10-15 tons of
refrigeration
$1000/ton/yr
$3.75/1000 IDS
GAC 8-mesh x 30 mesh
from PBS carbon
$2/lb carbon
$0.80/lb carbon +
freight expenses
Upgraded transfer pumps
between decanter and
feedwater tank
Shell and tube condenser
consists of 8 tubes,
3/4" 10. and 10' long
6 to 7 gpm for 24 hr/day
365 day/yr operation
48 gpm typical (37 gpm
wastewater, 11 gpm
caustic soda solution).
Transfer pumps rated
from 25 to 100 gpm, but
long pipe length reduces
maximum flow rate.
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S. Harkins Trip Report to Lucas
Page 4
12. Flow rate from decanter to feedwater tank 120-140 gpm. Pump is
rated at 140 gpm.
13. Distance between decanter tank and ~ 25' horizontal,
- storage tank-headspaces n)*~vert1c"a"1
14. Approximate cost estimate to connect ~ $2000 - $3000
the top of the decanter to the top of
the storage tank
15. Height of decanter tank secondary vent - 40'
condenser
16. Length of duct required to bring the - 150'
gases from secondary vent condenser to the
probable location of adsorption system
on ground level
17. Cost to install the duct work to connect ~ $4000 - $5000
condenser outlet stream to adsorber unit
18. Approximate value of recovered and ~ $250 - $300/ton
organic condensate in condenser - $0.125/lb of organics
RTI will prepare a technical and economic evaluation of control options
for the vent stream. Estimated costs and emission reductions will be
reported. The designs will be based on the maximum expected vent flow with
concentrations based on RTI's previous vent sampling. For all designs the
feedwater tank will be vented to a common header with the decanter tanks.
When liquid is pumped from the decanter tanks to the feedwater tank the gas
displaced from the feedwater tank will flow into the top of the decanter
tanks. This vent line will eliminate emissions associated with water transfer
from the decanters to the feedwater tank. When water is pumped into the
decanters gas from the top of the decanter tanks will be vented through the
control system. The control system will also handle the 12 1pm vent stream
from the primary steam stripper condenser.
A problem associated with any control system for the tank vents is the
tank operating pressure. The decanter tanks and feedwater tank were designed
for atmospheric operation. The conservation vents at the top of the tanks
open at very small pressure differences from atmospheric pressure. If an
installed control system places more than an extremely small back pressure on
the vent lines the conservation vents will open and vent displaced gas to the
atmosphere. Since these vents are on top of the tanks, operators would
probably not notice the discharge. An alarm system to indicate open
conservation vents could be installed to show a failure of an installed vent
control system.
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