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Preliminary sizing of VOC emission control systems for paint booths
PRELIMINARY SIZING OF VOC EMISSION CONTROL SYSTEMS FOR PAINT BOOTHS
by Robert E. Kenson Kenson Associates, West Chester. Pa.
When it is necessary to install a VOC emission control system on a paint spray booth, what are the size and weight of the system and what are its utility requirements are critical questions that must be answered quickly. The installation costs of the VOC emission control system depend upon its size and weight, and operating costs depend on the system utility requirements. Methods of quickly estimating the VOC emission control system preliminary size, weight, and utility requirements are, therefore, valuable tools for anyone contemplating installing such a system. The following guidelines will allow almost anyone to roughly estimate size, weight, and utility requirements for some of the commonly employed VOC emission control technologies. These preliminary estimates are believed to be accurate to within 25% of actual values and are designed for initial engineering and management report estimates, but are not recommended for final system installation design projects
CARBON ADSORBERS When the paint or coating applied in the spray booth contains some solvents that can be recovered and reused, even if only for fuel value, carbon adsorption can be a cost-effective VOC emission control system. In certain cases nonregenerable carbon systems, where the carbon is discarded and no solvent is recovered, are a low cost emission control option when the paint spray booth is used infrequently. Carbon adsorption systems are sized based on both the exhaust air flow and the solvent concentration of the VOC emission source. These two factors directly determine the amount of carbon adsorbent in the system, and this helps to determine the size of the adsorption vessels and the system fan. The electrical power to operate the system fan depends upon both the air flow of the adsorbers and the pressure drop through the carbon. The steam to regenerate the carbon and evaporate the adsorbed solvent depends upon the amount of carbon in the adsorption vessels. as does the cooling water to condense the steam and the solvent. The amount of carhon and the air flow also determine the size and weight of the adsorption vessels and that of the whole system. The amount of carbon required for a typical paint spray booth solvent emission control application can be determined by equation (I). where G is the pounds of granular carbon in the adsorption system and V is the air flow rate in cubic feet per minute (cfrn}.
G = 0.8835 X V
(I)
For a typical paint booth application, the fan motor electric requirement for the carbon adsorber system is given by equation (2) below, where E is the electric consumption in kilowatts and V is again the air flow in cfm. E = 1.12E - 03 X V
(2)
Equation (3) calculates S. the regeneration steam requirement in pounds per system operating hour, for the carbon adsorber in a typical paint spray booth application with G pounds of granular carbon in the system. S
=
01 X G
445
The cooling water requirement to condense the steam and solvent is given by the equation (4), where C is the cooling water requirement in gpm and S is again the carbon regeneration steam requirement in pounds per system operating hour. C = S/3
(4)
The weight of the carbon adsorber system in pounds, M; the system footprint in square feet, F; the length in feet, L; and the width in feet, W, for a typical paint spray booth application are determined by equations (5), (6), (7), and (8), respectively. V is again the paint booth exhaust air flow in cfm, M = 4.625 X V
(5)
F = 1.35 X (V)'"
(6)
L = (2 X F)li2
(7)
W
=
FIL
(8)
Carbon Adsorption System Example A paint spray booth has an exhaust air flow of 2,500 cfrn, which contains 250 ppmv of a solvent with an average molecular weight of 75. The adsorption capacity of the carbon is 5%, the adsorption cycle is 4 hours, the desorption cycle is one hour, the steam to carbon ratio is 0.4, and there are two carbon vessels. The required solvent emission control efficiency is 95%. Using equations (I) to (8), the installation requirements of the carbon adsorber are: W = 0.8835 x 2,250 = 1,988 Ib of carbon in the system E = 1.12E-03 x V = 2.52 kW per hour electrical power required S = 0.1 x 1,988 = 199 Iblhr regenerating steam required C = 199/3 = 66 gpm cooling water required M = 4.625 x 2,600 = 11,563 Ib weight for the carbon system F = 1.35 X (2,500fl1 = 248 ft2 footprint L = 12 x 248) 1/2 = 22.3 ft long W = 248/22.3 = 11.1 ft wide
REGENERATIVE THERMAL OXIDIZERS When the paint or coating applied in a spray booth consists of mixed solvents that cannot be recovered and reused, regenerative thermal oxidation may be a cost effective method of solvent destruction. Almost 95% of the heat of solvent combustion from the paint booth exhaust air can be recovered, along with most of the heat provided to initiate the solvent combustion. This can be done by passing the hot oxidizer exhaust gas through a bed of high-temperature heat transfer media, and then using the preheated media to heat up the booth exhaust solvent emissions to their combustion temperature. A twin-bed modular regenerative thermal oxidizer with a single valve switching the flow direction through the granular heat transfer media beds has been utilized in many paint spray booth solvent emission control applications. Either natural gas or electricity can be used to preheat the solvent contained in the paint booth exhaust to its combustion temperature. Typical solvent destruction efficiencies are greater than 98% when the combustion chamber temperature is J,500"F or higher. depending upon the VOCs present. The auxiliary energylfuel requirement for a typical paint spray booth application of a regenerative thermal oxidizer is determined by equation (9), where Q is the energy required in BTU per hour and Y again is the air flow in cfrn.
Q = 56 446
X
V
(9)
The fan motor electrical requirement for a typical paint spray booth application is given by equation (10) below, where E is the electrical consumption in kilowatts and V is the exhaust air flow in cfm. E
=
3.96E - 03
X
V
(10)
The weight of the regenerative thermal oxidizer system in pounds, M; the system footprint in square feet, F; the length in feet, L; and the width in feet, W, are given by equations (II), (12), (7), and (8), respectively. V is again the exhaust air flow in cfm. M = 5.5 X V
(II)
F = 2.6E - 02 X V
(12)
L = (2 X F)'/2
(7)
W = F/L
(R)
Regenerative Thermal Oxidizer Example A regenerative thermal oxidizer of 30,000 cfm air flow capacity is applied to control 250 ppmv of mixed paint solvent air emissions with the average solvent heat of combustion being 12,500 BTU per pound. Using equations (7) through (12), the system installation requirements are:
= 56 x 30,000 = 1,680,000 BTU per hour energy/fuel required E = 3.96E-03 x 30,000 = ]]9 kW per hour electrical energy required M = 5.5 x 30,000 = 150,000 Ib weight for the regenerative thermal oxidizer F = 2.6E-02 x 30,000 = 780 ft2 system footprint L = (2 x 780) 112 = 39.5 ft long W = 780/39.5 = 19.7 ft wide
Q
ROTARY CONCENTRATORS
A rotary zeolite or carbon concentrator, followed by a thermal oxidizer, can be a cost effective way to control the high air volume but very dilute solvent concentration in the emissions from large paint spray booths. The concentrator reduces the air volume by a factor of ten in order to minimize the operating cost of the thermal oxidizer which follows it. The paint booth exhaust air solvent emissions are first adsorbed onto a honeycomb wheel impregnated with a hydrophobic zeolite adsorbent. The wheel continuo sly rotates and the adsorbed solvents are desorbed, by a very small volume of hot air, in a separate desorption zone of the rotor before the wheel is saturated by the adsorbed solvents. The small volume of hot air with the concentrated solvent air emissions is then introduced into a small thermal oxidizer for final destruction of the VOCs. This type of system is used where there are mixed paint solvents in the spray booth exhaust that cannot be recovered and reused. A typical application of a rotary zeolite concentrator plus thermal oxidizer system would be where the mixed paint solvent emission concentration is less than 100 ppmv and the paint spray booth exhaust air volume is over 15,000 cfm. The auxiliary energy/fuel required to bring the preconcentrated paint spray booth solvent mixture to its thermal oxidation temperature is given by equation (13), where Q is the fuel energy required in BTU per hour and V again is the air flow in cfrn.
Q = 36
X
V
(13)
447
The fan motor electrical requirement for a typical paint spray booth application is given by equation (14) below, where E is the electrical consumption in kilowatts and V is the exhaust air tlow in cfrn.
E = 1.5E - 03
X
(14)
V
The weight of the rotary zeolite concentrator plus thermal oxidizer system in pounds, M; the system footprint in square feet, F; the length in feet, L; and the width in feet. W. are given by equations (15), (16), (17), and (8). respectively.
= 244
X (V)'12
(15)
F = 2.95 X (V)'12
(16)
L = (3 X F)'12
(17)
M
W = FIL
(8)
Rotary Concentrator Example A rotary zeolite concentrator system of 40.000 cfm air tlow capacity is used to control 100 ppm v of mixed paint solvent air emissions with an average solvent heating value of 12.500 BTU/pound of solvent. Using equations (7) to (8) and (13) to (16). the system installation requirements are:
Q
= 36 x 40,000 = 1,440,000 BTU per hour fuel energy required E = 1.5E-03 x 40,000 = 60 kilowatts per hour electrical energy required M = 244 X (40,000)1/2 = 48,800 Ib concentrator system weight F = 2.95 X (40,000)1/2 = 590 ft 2 system footprint L = n x 590)112 = 42.0 ft long W = 590/42 = 14.0 ft wide
CONCLUSIONS Simple equations, as shown above, can be used to determine the preliminary installation requirements such as size, weight, and utility needs for paint spray booth solvent emission control systems. Once this is done initial decisions can be made as to where to locate this equipment and what system technology to select. These simple equations also can be used to generate preliminary cost estimates for system installation.
The Technology of Anodizing Aluminum by A.lr: 1J""c 4111
pa~cs
$210.1111
SLW"/:,[)rII01\' This valuable book bas been cornplctclv re-edited and considers significant new developmcnrs in anodizing tcchn{)l()g~" The expanded volume will sarisfv the anudizcr who require- more detailed technology. After an introduction, the reader is presented with practical application of the new rcchnologv, and the nature of the industry with carnal investment appraisal, budgeting and cost control. An excellent summary of anodi2ing technologies in clear language encompassing the advice of experienced technicians.
Send Orders to: METAL FINISHING, (,(,(1 White PI"ins Rd., Tarn-town, I\Y )11591-5103 For faster service. call (914) 33.1-2'i7 R or L\X your order to (914) 333-2.1711 All book orders must be prepaid. Please include $).(10 shippIng and handling for dclivcrv of each book via UPS 10 the US., 51O.()(l for each book shipped express to Canada; and S20.0U for each hook shirred express to all other countries.
449
by Robert E. Kenson Kenson Associates, West Chester. Pa.
When it is necessary to install a VOC emission control system on a paint spray booth, what are the size and weight of the system and what are its utility requirements are critical questions that must be answered quickly. The installation costs of the VOC emission control system depend upon its size and weight, and operating costs depend on the system utility requirements. Methods of quickly estimating the VOC emission control system preliminary size, weight, and utility requirements are, therefore, valuable tools for anyone contemplating installing such a system. The following guidelines will allow almost anyone to roughly estimate size, weight, and utility requirements for some of the commonly employed VOC emission control technologies. These preliminary estimates are believed to be accurate to within 25% of actual values and are designed for initial engineering and management report estimates, but are not recommended for final system installation design projects
CARBON ADSORBERS When the paint or coating applied in the spray booth contains some solvents that can be recovered and reused, even if only for fuel value, carbon adsorption can be a cost-effective VOC emission control system. In certain cases nonregenerable carbon systems, where the carbon is discarded and no solvent is recovered, are a low cost emission control option when the paint spray booth is used infrequently. Carbon adsorption systems are sized based on both the exhaust air flow and the solvent concentration of the VOC emission source. These two factors directly determine the amount of carbon adsorbent in the system, and this helps to determine the size of the adsorption vessels and the system fan. The electrical power to operate the system fan depends upon both the air flow of the adsorbers and the pressure drop through the carbon. The steam to regenerate the carbon and evaporate the adsorbed solvent depends upon the amount of carbon in the adsorption vessels. as does the cooling water to condense the steam and the solvent. The amount of carhon and the air flow also determine the size and weight of the adsorption vessels and that of the whole system. The amount of carbon required for a typical paint spray booth solvent emission control application can be determined by equation (I). where G is the pounds of granular carbon in the adsorption system and V is the air flow rate in cubic feet per minute (cfrn}.
G = 0.8835 X V
(I)
For a typical paint booth application, the fan motor electric requirement for the carbon adsorber system is given by equation (2) below, where E is the electric consumption in kilowatts and V is again the air flow in cfm. E = 1.12E - 03 X V
(2)
Equation (3) calculates S. the regeneration steam requirement in pounds per system operating hour, for the carbon adsorber in a typical paint spray booth application with G pounds of granular carbon in the system. S
=
01 X G
445
The cooling water requirement to condense the steam and solvent is given by the equation (4), where C is the cooling water requirement in gpm and S is again the carbon regeneration steam requirement in pounds per system operating hour. C = S/3
(4)
The weight of the carbon adsorber system in pounds, M; the system footprint in square feet, F; the length in feet, L; and the width in feet, W, for a typical paint spray booth application are determined by equations (5), (6), (7), and (8), respectively. V is again the paint booth exhaust air flow in cfm, M = 4.625 X V
(5)
F = 1.35 X (V)'"
(6)
L = (2 X F)li2
(7)
W
=
FIL
(8)
Carbon Adsorption System Example A paint spray booth has an exhaust air flow of 2,500 cfrn, which contains 250 ppmv of a solvent with an average molecular weight of 75. The adsorption capacity of the carbon is 5%, the adsorption cycle is 4 hours, the desorption cycle is one hour, the steam to carbon ratio is 0.4, and there are two carbon vessels. The required solvent emission control efficiency is 95%. Using equations (I) to (8), the installation requirements of the carbon adsorber are: W = 0.8835 x 2,250 = 1,988 Ib of carbon in the system E = 1.12E-03 x V = 2.52 kW per hour electrical power required S = 0.1 x 1,988 = 199 Iblhr regenerating steam required C = 199/3 = 66 gpm cooling water required M = 4.625 x 2,600 = 11,563 Ib weight for the carbon system F = 1.35 X (2,500fl1 = 248 ft2 footprint L = 12 x 248) 1/2 = 22.3 ft long W = 248/22.3 = 11.1 ft wide
REGENERATIVE THERMAL OXIDIZERS When the paint or coating applied in a spray booth consists of mixed solvents that cannot be recovered and reused, regenerative thermal oxidation may be a cost effective method of solvent destruction. Almost 95% of the heat of solvent combustion from the paint booth exhaust air can be recovered, along with most of the heat provided to initiate the solvent combustion. This can be done by passing the hot oxidizer exhaust gas through a bed of high-temperature heat transfer media, and then using the preheated media to heat up the booth exhaust solvent emissions to their combustion temperature. A twin-bed modular regenerative thermal oxidizer with a single valve switching the flow direction through the granular heat transfer media beds has been utilized in many paint spray booth solvent emission control applications. Either natural gas or electricity can be used to preheat the solvent contained in the paint booth exhaust to its combustion temperature. Typical solvent destruction efficiencies are greater than 98% when the combustion chamber temperature is J,500"F or higher. depending upon the VOCs present. The auxiliary energylfuel requirement for a typical paint spray booth application of a regenerative thermal oxidizer is determined by equation (9), where Q is the energy required in BTU per hour and Y again is the air flow in cfrn.
Q = 56 446
X
V
(9)
The fan motor electrical requirement for a typical paint spray booth application is given by equation (10) below, where E is the electrical consumption in kilowatts and V is the exhaust air flow in cfm. E
=
3.96E - 03
X
V
(10)
The weight of the regenerative thermal oxidizer system in pounds, M; the system footprint in square feet, F; the length in feet, L; and the width in feet, W, are given by equations (II), (12), (7), and (8), respectively. V is again the exhaust air flow in cfm. M = 5.5 X V
(II)
F = 2.6E - 02 X V
(12)
L = (2 X F)'/2
(7)
W = F/L
(R)
Regenerative Thermal Oxidizer Example A regenerative thermal oxidizer of 30,000 cfm air flow capacity is applied to control 250 ppmv of mixed paint solvent air emissions with the average solvent heat of combustion being 12,500 BTU per pound. Using equations (7) through (12), the system installation requirements are:
= 56 x 30,000 = 1,680,000 BTU per hour energy/fuel required E = 3.96E-03 x 30,000 = ]]9 kW per hour electrical energy required M = 5.5 x 30,000 = 150,000 Ib weight for the regenerative thermal oxidizer F = 2.6E-02 x 30,000 = 780 ft2 system footprint L = (2 x 780) 112 = 39.5 ft long W = 780/39.5 = 19.7 ft wide
Q
ROTARY CONCENTRATORS
A rotary zeolite or carbon concentrator, followed by a thermal oxidizer, can be a cost effective way to control the high air volume but very dilute solvent concentration in the emissions from large paint spray booths. The concentrator reduces the air volume by a factor of ten in order to minimize the operating cost of the thermal oxidizer which follows it. The paint booth exhaust air solvent emissions are first adsorbed onto a honeycomb wheel impregnated with a hydrophobic zeolite adsorbent. The wheel continuo sly rotates and the adsorbed solvents are desorbed, by a very small volume of hot air, in a separate desorption zone of the rotor before the wheel is saturated by the adsorbed solvents. The small volume of hot air with the concentrated solvent air emissions is then introduced into a small thermal oxidizer for final destruction of the VOCs. This type of system is used where there are mixed paint solvents in the spray booth exhaust that cannot be recovered and reused. A typical application of a rotary zeolite concentrator plus thermal oxidizer system would be where the mixed paint solvent emission concentration is less than 100 ppmv and the paint spray booth exhaust air volume is over 15,000 cfm. The auxiliary energy/fuel required to bring the preconcentrated paint spray booth solvent mixture to its thermal oxidation temperature is given by equation (13), where Q is the fuel energy required in BTU per hour and V again is the air flow in cfrn.
Q = 36
X
V
(13)
447
The fan motor electrical requirement for a typical paint spray booth application is given by equation (14) below, where E is the electrical consumption in kilowatts and V is the exhaust air tlow in cfrn.
E = 1.5E - 03
X
(14)
V
The weight of the rotary zeolite concentrator plus thermal oxidizer system in pounds, M; the system footprint in square feet, F; the length in feet, L; and the width in feet. W. are given by equations (15), (16), (17), and (8). respectively.
= 244
X (V)'12
(15)
F = 2.95 X (V)'12
(16)
L = (3 X F)'12
(17)
M
W = FIL
(8)
Rotary Concentrator Example A rotary zeolite concentrator system of 40.000 cfm air tlow capacity is used to control 100 ppm v of mixed paint solvent air emissions with an average solvent heating value of 12.500 BTU/pound of solvent. Using equations (7) to (8) and (13) to (16). the system installation requirements are:
Q
= 36 x 40,000 = 1,440,000 BTU per hour fuel energy required E = 1.5E-03 x 40,000 = 60 kilowatts per hour electrical energy required M = 244 X (40,000)1/2 = 48,800 Ib concentrator system weight F = 2.95 X (40,000)1/2 = 590 ft 2 system footprint L = n x 590)112 = 42.0 ft long W = 590/42 = 14.0 ft wide
CONCLUSIONS Simple equations, as shown above, can be used to determine the preliminary installation requirements such as size, weight, and utility needs for paint spray booth solvent emission control systems. Once this is done initial decisions can be made as to where to locate this equipment and what system technology to select. These simple equations also can be used to generate preliminary cost estimates for system installation.
The Technology of Anodizing Aluminum by A.lr: 1J""c 4111
pa~cs
$210.1111
SLW"/:,[)rII01\' This valuable book bas been cornplctclv re-edited and considers significant new developmcnrs in anodizing tcchn{)l()g~" The expanded volume will sarisfv the anudizcr who require- more detailed technology. After an introduction, the reader is presented with practical application of the new rcchnologv, and the nature of the industry with carnal investment appraisal, budgeting and cost control. An excellent summary of anodi2ing technologies in clear language encompassing the advice of experienced technicians.
Send Orders to: METAL FINISHING, (,(,(1 White PI"ins Rd., Tarn-town, I\Y )11591-5103 For faster service. call (914) 33.1-2'i7 R or L\X your order to (914) 333-2.1711 All book orders must be prepaid. Please include $).(10 shippIng and handling for dclivcrv of each book via UPS 10 the US., 51O.()(l for each book shipped express to Canada; and S20.0U for each hook shirred express to all other countries.
449