2016 ECI 150 Particulate Emission Control for CaBTaC University of California, Davis

UC Consulting

Members: Hayden Lee, Alexander Wang, Tak Shun Li

Table of Contents

1. Executive Summary………………………………………………………....1

2. Project Background………………………………………………………….2

3. Inflow Condition…………………………………………………………….2

4. Design of Cyclone…………………………………………………………...3

a. Cost Estimate…………………………………………………………4

5. Design of Cooler………………………………………………………….....4

a. Shell-And-Tube Exchanger…………………………………………...4

b. Water injection Cooler………………………………………………..4

c. Cost Estimate…………………………………………………………4

d. Suggestion…………………………………………………………….5

6. Design of final control device……………………………………………….5

a. Pulse-Jet Baghouse…………………………………………………...5

b. ESP…………………………………………………………………....6

c. Cost Estimate…………………………………………………………6

d. Suggestion…………………………………………………………….7

7. Total Cost Summary…………………………………………………………7

8. Appendix……………………………………………………………….........8

a. Appendix A: Tables and Graphs……………………………………...8

b. Appendix B: Equations……………………………………………...11

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Executive Summary

The objective is to reduce particulate emission coming from natural borax and talc drying/collecting process in the Cappa Borax and Talc Company (CaBTaC) plant site. It is necessary to include a two parallel and identical cyclone, a cooler, and a final control device that is either a baghouse or an ESP as a complete design. As our goal, we want to optimize this treatment system by achieving minimum cost with maximum efficiency.

Before the final control device, a cyclone should be implemented as a pretreatment to remove some portion of particles to reduce particle loadings in final control device. After comparing several different alternatives, we suggest using a high efficiency cyclone with 1.3m body diameter to achieve a 67% total particulate removal. The TIC (total installment cost) for the cyclone is $91,600.

As requested by CaBTaC, a cooler is implemented prior to the final control device to cool air stream from 343°C to 177°C in order to prevent heat damage in the latter devices. Using the shell-and-tube heat exchanger recycles heat energy into dryer which can save energy while reducing fuel cost. In fact, the heat exchanger can save 6,600 gallons of fuel, saving up to $165,000 each year. The TIC for the heat exchanger is $100,000. To achieve the required particulate emission, our suggestion for final control device is a pulse-jet baghouse with 161 number Nomex bags. Baghouse is well known for its high efficiency in particulate removal, and is ideal for a moderate loading as present in CaBTaC. The total cost for the suggested baghouse design would be approximately $234,406 upfront cost. This value takes into consideration of the compressor capital cost disregarding the fan cost. It should be emphasized that the baghouse is a significantly much lower cost in comparison to the ESP and have an efficiency that is just as high. The annual operation cost for baghouse, including depreciation, maintenance, power, taxes and insurance, is $56,000. With these design, our suggested system will guarantee the particulate emission well below 10 kg/hr. The total installment cost of the entire system is $426,000 and $56,000 in annual operation cost. Fortunately, fuel saving from heat exchanger is $165,000, which helps save $110,000 in total each year. As a result, we have a system is highly cost effective and capable of delivering the required performance as requested by CaBTaC.

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Background:

Mixture of natural talc and borax is refined, crushed, and dried into small pieces for use in industrial applications within the Cappa Borax and Talc Company plant. With such intensive process, this produces large amounts of dust that needed to be treated and controlled before being exhausted out of the system. As such, the primary goal is to design a filter that minimizes particulate emission as much as possible.

Objectives and Targets:

➢ Particulate emission coming from the plant must be reduced to 10kg/hr

➢ A cyclone and cooler must be included ➢ Cyclone overall efficiency must at least be 65%~75% so that cost of cleaning and

powering the system is optimized and not too excessive ➢ Cooler must reduce exhaust gas temperature ➢ A final control device must be decided between between a baghouse or electrostatic

precipitator (ESP) ➢ Cost must be as low as possible with an adequate overall efficiency

Inflow Condition:

The particulate emission comes mainly from the talc and borax crusher, which crushes the ores into solids smaller than 1centimeter. Although most of the solid goes into storage, about 0.2% of the dry solids goes into exhaust gas at 343°C . The following figure is a rough layout of the crusher and dryer system (refer to Table #1 in

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appendix for complete mass balance for each stream):

Figure A: schematics of the crusher system Stream 6 is the exhaust gas that will be treated by our design. The exhaust gas coming in from the dryer consists of 920 kg/hr of solid particles. To reach the 10 kg/hr emission requirement, the system has to achieve at least 98.9% overall efficiency.

Cyclone: Requirements from CaBTaC are taken into consideration, entailing: overall efficiency to be between 65% to 75%, maximum pressure drop to be 1994 Pa, and the gas inlet velocity to be smaller than 30.5m/s. The least cost with the highest efficiency among some common cyclones is chosen. In order to make a fairer comparison, different types of cyclone are analyzed which includes high efficiency, conventional ,and high throughput cyclones. It is found that the efficiencies of cyclones increase with flow velocity (see equation # 1, #2 and #3 for calculation detail). Therefore, we use 30.5 m/s, the maximum inlet velocity given by the CaBTaC, in all our cyclone calculations. Because body diameter depends on flow rate and inlet velocity, and the inlet gas flow rate is fixed at 46,043 m3/hr at 343°C, body diameter has to be equal to 1.3m at the suggested inlet velocity. The possibility of using the high throughput cyclones was eliminated due to their low total efficiencies, which are 49% and 48%. This value is much lower than the required 65% and so this is quickly ruled out. The total efficiencies of the two conventional cyclones, on the other hand, are slightly less than 65% while the total efficiencies of the two high efficiency cyclones are very close to 65%. As determined in Table #2, the possibility of using high efficiency (B), conventional (C), and conventional (D) is eliminated as both of them show pressure drops greater than 1994 Pa. Table #2

Cyclones Stairmand high

efficiency (A)

Swift high efficiency

(B)

Lapple conventional

(C)

Swift conventional

(D)

Stairmand high

throughput (E)

Swift high throughput

(F)

Total efficiencies

(%)

67 68 65 63 49 48

Pressure drop (Pa)

1612 2328 2016 2016 2016 2007

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Therefore, Stairmand high efficiency cyclone is the best cyclone choice to our final design. The mass flow rate of particles in exit gas is 304 kg/hr with a loading rate of 6.6 g/ m3. Cost Estimate: The total installment cost of this cyclone is $91,622 in 2008 dollars. It is important to mention that the total installed cost of cyclone includes both the cost of the cyclone system (Pc) and the cost of rotary airlock valve (Pv).

Cooler: The major function of the cooler is to cool the air stream from 343°C to 177°C in order to prevent heat damage and SO3 or H2O condensation in the latter final control devices. There are two alternatives: Shell-and-Tube Exchanger and Water injection Cooler. Shell-and-Tube Exchanger can recycle heat collected from hot air and reuse it in the dryer to save fuel cost; however, it takes up more space and is more costly. Water injection cooler is more efficient and economical, but it introduces humidity to the air stream, which limits its lowest cooling temperature to avoid condensation. Shell-and-Tube Exchanger: The major advantage using a Shell-and Tube Exchanger is its energy recycle feature. By calculating the enthalpy of air and vapor, there are about 4.73x106 kJ of energy is exchanged each year. Given that fuel lower heating value (LHV) is 41,868 kJ/kg and heat exchanger efficiency is 80%, the cooler system can save 6,600 gallons of fuel each year by utilizing the exchanged energy. By calculating the log mean temperature difference and recycled energy, about 445 m2 heat transfer area is required to transfer the required energy. Water Injection Cooler: Water injection cooler is needed to cool the air stream to 204°C instead of 177°C to avoid condensation. From enthalpy calculation, the cooler require 376 gallons of water per hour to cool the exhaust gas. Cost Estimate: Heat exchanger costs $100,000 and water injection cooler costs $30,000 for installation. Water injection cooler has a lower installation cost, but it does not produce saving. Assuming fuel cost average is $2.5/gal and the facility runs 2,500 hours per year, heat exchanger can save $165,108 each year (equation #4). Calculating the payback period of the coolers, water injection cooler takes 20 years to payback, while heat exchanger only takes about 1 year and 2 months (1.13 years).

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Suggestion: Considering the significantly shorter payback period and lower cooling temperature, heat exchanger would thus be the best option for the system.

Final Control Devices: Two commonly applied final control devices are considered: Baghouse and Electrostatic Precipitator (ESP). Baghouse has the highest collection efficiency of any pollution control device. However, it is vulnerable to hot or chemically corrosive gases and costs energy to overcome its high pressure difference. ESP requires less energy and is less affected by corrosion, but there’s strict limitation in solid particles’ resistivity, which would affect its efficiency. Baghouse: Among pulse-jet, reverse-air and shaker baghouse, pulse-jet baghouse can operate at the highest filtering velocity with the lowest capital cost. Thus, we suggest using pulse-jet baghouse. Due to the high temperature (177oC) from incoming gas, only a limited options of fabrics can be used, namely Teflon, glass fiber, and Nomex. Teflon is expensive, and glass fiber has poor abrasion resistance. As a result, Nomex is the ideal material for the given scenario. The dimension of the bag is suggested to be 15.24cm x 2.44m (6in x 8ft) to avoid the energy lost in compressed air in longer bags. The system can withstand filtering velocity as high as 3.35 m/min and as low as 2.74m/min for Talc particles. Assuming gas is cooled to 149 oC, its flow rate will be 525 m3/min. Each bag will have an area 1.2m2, therefore, dividing flow rate by velocity and area of each bag, it is found that the baghouse requires at least 132 or at most 161 bags to achieve the filtering velocity. We suggest using 161 bags because it requires lower filtering velocity, which results in lower average pressure drops and longer bag life. We recommend not implementing stainless-steel add-on (SSA) and insulation (INS). SSA is to prevent corrosion. SO3, the only corrosive chemical in the air stream and has very low concentration. Therefore, SSA is not necessary. INS, on the other hand, is to prevent temperature drop and condensation of SO3 and H2O. As mentioned before, SO3 has a small concentration, so it is not a concern. Water vapor will not condense because temperature is well above dew point, which is around 66oC according to psychometric chart. Temperature drop within the baghouse might not reach the condensation temperature, thus INS is not required as well. An air compressor is required to produce pulse-jet. 4.25 m3/min air should be applied at 790,801Pa to clean up the bags efficiently. Having a compression efficiency of 50%, the air compressor requires at least 40 kW energy to achieve these conditions.

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Figure B, Bags layout in baghouse

ESP: Dividing the total particle mass penetrated cyclone by 10 kg/hr, the total collection efficiency for ESP has to be above 96.7% in order to reach 98.9% overall efficiency. From pilot testing (Table #5), it is determined that drift velocity has to be 0.079 m/s. Using this value along with typical values of the design parameter, we suggest having 376 m2 of collection area using six 5.5m x 7m (WxH) plates, evenly spaced out 0.15m from each other. Corona power should be around 1.92 kW and a fan power about 1.68 kW. There should be 5 ducts, 1 mechanical field and 2 bus sections to reach the required efficiency. Compartment wise, we suggest implementing one. This decision is based on the low operation time (2500 hours/year), which means a baghouse failure would be unlikely and less impactful on company’s operation. Having only one compartment is also the cheapest. Cost Estimate: Total installment cost is $234,406 for baghouse, and $641,980 for ESP. Annual operation cost for baghouse, including tax, maintenance, depreciation, power, and bag replacement, is $56,136.8 Annual operation cost for ESP, including tax, maintenance, depreciation, and power is $110,035.6. Suggestion: Considering its lower installment and operation cost as well as higher efficiency, baghouse has a significant advantage over ESP. As a result, baghouse is selected as the final control device.

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However, CaBTaC should be extremely cautious during baghouse operation to avoid dust explosion, as it lead to detrimental damage to company’s property. This can happen if temperature is not well-controlled within the required range as described above.

Total Cost Summary:

Figure C, Schematics of the filtration system

The total cost of the entire system, including installment cost of cyclone, cooler, and baghouse, is $426,028. Total annual operation cost is $59,932. Fuel saving each year would be $165,108. Note: All cost estimate in the report is displayed in 2008 dollar values.

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Appendix A: Tables and Graphs Table #1 Material Balance Table

Material Balance Table

Component, thousand kg/hr

Stream Number

Dry Solid N2 O2 CO2 H2O S Other Total

1 47.83 0 0 0 4.17 0 0 52

2 46 0 0 0 4 0 0 50

3 0 0 0 0 0 0.0008 0.27* 0.27

5 45.08 0 0 0 0.09 0 0 45.17

4 0 14.98 4.6 0 0 0 0.274** 19.86

6 0.92 14.98 3.71 0.873 4.2 0 0.2756*** 24.96

Note: *consists of 0.238 thousands kg/hr Carbon and 0.032 thousands kg/hr Hydrogen; **consists of 0.274 thousands kg/hr Argon; ***consists of 0.274 thousands kg/hr Argon and 0.0016 thousands kg/hr SO2 Table #2 Total efficiencies and pressure drop of the six cyclones considered

Cyclones high efficiency

(A)

high efficiency

(B)

conventional

(C)

conventional

(D)

high throughput

(E)

high throughput

(F)

Total efficiencies (%)

67 68 65 63 49 48

Pressure drop (Pa)

1612 2328 2016 2016 2016 2007

Table #3 Weight % collected and weight % passed for the high efficiency cyclone (A)

size range (10^-6 m)

% efficiency (%)

weight % in size range (%)

weight % collected (%)

weight % passed (%)

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0-2 2.3 1 0.02 1

2-4 17.5 9 1.6 7.4

4-6 37.1 10 3.7 6.3

6-10 60.2 30 18.1 11.9

10-18 82.2 30 24.7 5.3

18-30 93.2 14 13.0 1

30-50 97.4 5 4.9 0.1

>50 98.3 1 1 0.02

Sum: 66.95 33.05

Table #4 original weight distribution vs weight distribution after cyclone installation

size range (10^-6 m)

original weight distribution (%)

weight distribution after cyclone installation (%)

0-2 1 3

2-4 9 22.4

4-6 10 19

6-10 30 36

10-18 30 16

18-30 14 2.9

30-50 5 0.4

>50 1 0.05

Table #5 pilot-scale test results for the pilot-scale ESP

inlet loading 5.0 gr/ft^3

outlet loading 0.10 gr/ft^3

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gas velocity 5 ft/sec

corona power 12.0 W

gas flow rate 100 ft^3/min

collection surface area 25 ft^2

Graph #1: Weight Distribution before and after cyclone installation

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Appendix B: Equations equation #1: dpc = ((9 u W)/ ((2 π Ne Vi (ρp- ρg))1/2

where u= gas viscousity W= length of tangential inlet duct Ne= number of effective turns Vi= gas inlet velocity ρp= density of particle ρg= gas density equation #2: nj= 1/(1+(dpc/dpj)2 where nj= collection efficiency for a particular particle size range equation #3: no= ∑ nj mj where no= overall collection efficiency mj= mass fraction of particles in particular size range note: dpc ↓ as Vi increases nj ↑ as dpc ↓ no ↑ as nj ↑ Equation #4: $saved/yr = (E recycled/ (LHV fuel* ρfuel))* Cost fuel per unit volume* (2500 hrs/ yr) (Fuel Cost Saved) where $ saved/yr= fuel cost saved per year ρ fuel= fuel density Cost fuel per unit volume = fuel cost per unit volume

Works Cited

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Cooper, C. David., and F. C. Alley. Air Pollution Control: A Design Approach. Long Grove (IL): Waveland, 2011. Print. Vallero, David. "Fundamentals of Air Pollution." Google Books. Academic Press, n.d. Web. 01 Mar. 2016.