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How to Size Eductors for In-Line Heating |
| All eductors heat by condensing steam into the liquid being heated. Due to differences in the design of each eductor, performance will vary for different models. A set of general rules is provided to calculate the amount of steam needed to heat any flow of liquid. To calculate the approximate steam flow required, some of the correction factors will be ignored. If a precise number is needed for the consumption of steam, use a steam table to determine the exact BTUs per Lb of steam. In general this will effect the calculation less than 3%. |
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| Formulas: |
| Qs = Qm x 8.33 x ∆T/1100 BTU/Lb |
| AT = Qs x 1100/Qmx8.33 |
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| Terms For Formula: |
| Qs = Steam flow in Lb/Min required to heat liquid |
| Qm = Liquid flow in GPM |
| Sg = Specific gravity of inlet liquid |
| 8.33 = Density of water in Lb/Gal. If the specific gravity or specific heat of the liquid is different from 1, multiply 8.33 by the actual values to correct the calculation. |
| ∆T = Differential temperature in degrees F |
| 1100 = BTUs per Lb of steam average. If a more accurate number is required, calculate this number from a set of steam tables. |
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| Parameters Required to Size an Eductor |
Liquid Inlet Conditions |
- What is the Liquid?
- Liquid Pressure
- Incoming Liquid Temperature
- Liquid Flow
- Desired Temperature Rise
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| Heating or Steam Inlet |
- Steam Pressure
- Steam Quality (is it saturated or superheated?) Outlet
- Maximum Outlet Pressure
- Desired Outlet Temperature
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| Procedures for Sizing MLE, MLH Eductors for In-line Heating |
| Step 1. Calculate the amount of steam required to heat your liquid flow. Use the calculation Qs = QM x 8.33 x ∆T/110 |
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Step 2. Locate the row on the MLE or MLH performance table that corresponds to the liquid motive pressure. Follow the row selected until the temperature rise meets or exceeds your desired temperature rise.
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| Step 3. Take the motive liquid flow desired, divide by the flow given in the table located 2 lines below the temperature rise chosen in Step 2. This will give a Desired Sizing Factor (S.E). Choose the eductor size that meets or exceeds the estimated S.F. from the S.F. table. |
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| Step 4. Determine if the steam pressure at this point is equal to or less than the steam pressure available. |
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| Step 5. Check the outlet pressure at this point to be sure it meets or exceeds your required outlet pressure. (This is the outlet pressure with the steam running. If this is an intermittent heating operation, use the outlet pressure listed with the steam at 0 PSIG) |
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| Example: |
| Motive Flow Qm 90 GPM |
| Motive Pressure 60 PSIG |
| Motive Temperature 80°F |
| Heating (Steam) Pressure 100 PSIG |
| Steam Condition Saturated |
| Outlet Pressure 30 PSIG Desired Outlet Temperature To 150° F |
| Desired Temperature Rise ∆T = 150 - 85 = 65° F |
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| Step 1. |
| Qs = 90 x 8.33 x 65/1100 |
| Qs = 44.3 Lb per Min. Steam |
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| Step 2. In the model MLH at 60 PSIG and 65° F temp. rise the 1-1/2" unit flows 30 GPM of inlet liquid. |
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| Step 3. |
| S.E = 90/30 |
| S.F. = 3.0 |
| In this case, the MLH 2-1/2" with a S.E of 3.17 should be chosen. |
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| Step 4. Is the steam pressure at this point less than the steam pressure available? If not, examine another unit. This is less than the 100 PSIG available. |
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| Step 5. The outlet pressure in the performance table at this point reads 50 PSIG. This exceeds the required 30 PSIG. |
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| Calculations of Actual Performance: |
| For MLH 2-1/2" chosen above |
| Qm = 29 (from Table) x 3.17 S.E = 91.9 GPM |
| Qs =15.6 (from Table) x 3.17 S.E = 49.4 Lb /min steam |
| ∆T = (49.4 x 1100)/(91.9 x 8.33) = 71.0° F |
As you can see, the performance of the actual unit will vary slightly from the calculated sizing. If the 71° is too much, the steam pressure may need to be reduced to achieve proper performance.
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| Procedures for Sizing ULJ Eductors for In-Line Heating |
| If using a ULJ, the amount of liquid flow is determined by the pressure drop (∆P). |
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| Step 1. Calculate the amount of steam required to heat the liquid flow. Use the following calculation Qs = Qm x 8.33 x ∆T/ 1100. |
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| Step 2. Locate the row on the ULJ performance table that corresponds to the liquid pressure. Move across this row until under the column which represents the steam pressure that is equal to or lower than your actual pressure available (Ps). This is your steam flow. |
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| Step 3. Take the steam flow desired (Qs) divided by the flow from the table found in Step 2. This will give a Desired Sizing Factor (S.F.). Choose the eductor with a Tabulated S.F. that meets or exceeds the Desired S.E |
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Step 4 To determine the outlet pressure ( Po), calculate the pressure drop (delta P) using the formula below and the S.F. selected in Step 3. Subtract the AP from the pressure at the motive connection (Pm). The result is the outlet pressure (Po).
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| Step 5. To determine the actual temperature rise AT (° F), use the formula below with actual motive and suction flows (GPM) as the input values. |
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| Formula's |
∆P = (Qm/(14.14 x S.E))
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| ∆T =Qsx1100/Qmx8.33 |
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