1. RFQ Toolbox Nicky Byer, Applications Engineer nicky.byer@munters.com
Dan McClung, Applications Engineer
September 29, 2012

2. Heat Recovery: Knowing what to ask
Hot side inlet temperature (operating/design)
Cold side inlet temperature
Required performance: effectiveness, cold outlet, or hot outlet
Pressure drop requirements
Gas composition / humidity ratio
Max differential pressure
Specific material requirements
Size limitations / flow arrangement
Corrosives (chlorine, sulfur, etc.)
Particulates
Condensables
Accessories (access doors, water wash, sonic horn, etc.)
Payback information ($/MMBTU and $/kWh)
RFQ Toolbox
September 29, 2012

3. Filling Out the Heat Exchanger Questionnaire
Request for Quotation
Filling Out the Heat Exchanger Questionnaire
RFQ Toolbox
September 29, 2012

4. RFQ Toolbox
September 29, 2012

5. RFQ Toolbox
September 29, 2012

6. Cost of heat exchanger X2
RFQ Toolbox
September 29, 2012

7. Major Factors that affect Heat Exchanger Unit Cost
Airstream Properties
Temperature
Corrosives, Particulates, etc.
Max pressure differential
Effectiveness
Size Limitations
Allowable Pressure Drop (DP) –CRITICAL
RFQ Toolbox
September 29, 2012

8. Pressure Drop Example
Customer wants to use the exhaust stream from a 10,000 SCFM incinerator with outlet temperature of 1000°F to preheat a makeup airstream at 70°F.
Heat Exchanger Specification:
304 SS Construction, UI flow pattern, 70% Effective, Fully Insulated unit with Expansion Joints
If unit has 1.5” W.C. DP per side, Total 3” W.C. DP then: Unit Cost = $92,255 NET
If unit has 3” W.C. DP per side, Total 6” W.C. DP then: Unit Cost = $74,191 NET
Additional Unit Cost for Lower DP = $18,064 (~20%)
RFQ Toolbox
September 29, 2012

9. RULES OF THUMB Converting ACFM and SCFM SCFM=ACFM * [530/(460+T)]
ACFM=SCFM * [(460+T)/530]
RFQ Toolbox
September 29, 2012

10. RULES OF THUMB Converting #/Hr to SCFM (#/Hr.) / 4.5 = SCFM
* 4.5 = (Density of Standard Air, #/Cubic Foot) * 60 Min./Hr.
RFQ Toolbox
September 29, 2012

11. RULES OF THUMB Converting Temperature
Celsius to Fahrenheit °F= 1.8 X °C + 32
Fahrenheit to Celsius °C= (°F - 32)/ 1.8
RFQ Toolbox
September 18, 2018

12. RULES OF THUMB Converting Pressure psig to psia Psig + 14.7
psia to psig Psig – 14.7
psig to inches of H Psig X 27.7
inches of H20 to psig inches of H20/ 27.7
RFQ Toolbox
September 18, 2018

13. RULES OF THUMB
tho
tci
thi
tco
RFQ Toolbox
September 18, 2018

14. RULES OF THUMB Stacks Measure free flow area
Measure velocity with flow meter
Measure temperature with IR gun or TC
Calculate BTU’s available
RFQ Toolbox
September 18, 2018

15. RULES OF THUMB Energy Available in Exhaust
BTU/Hr = Mass Flow * Cp * DT or
BTU/Hr = 1.08 *SCFM* DT
DT = Desired Exhaust Temperature change
Mass Flow = #/Hr
Cp = Average Specific Heat
SCFM = Standard Cubic Feet per Minute
RFQ Toolbox
September 18, 2018

16. RULES OF THUMB Stacks Rule of thumb is 1000 FPM minimum velocity
Higher velocities are often seen on stacks with fumes for dilution such as from exhaust hoods or oxidizers
Max is typically in the FPM range
RFQ Toolbox
September 18, 2018

17. Prices this year are the lowest they have been in the past 10 years.
RULES OF THUMB
Natural Gas Prices
Good Internet Source:
Prices this year are the lowest they have been in the past 10 years.
RFQ Toolbox
September 18, 2018

18. Fuel costs are currently approximately $5.00/MMBTU
RULES OF THUMB
1 Therm = 100,000 BTU's.
$5/MMBTU’s = $0.50/Therm
Fuel costs are currently approximately $5.00/MMBTU
RFQ Toolbox
September 18, 2018

19. Equipment Cost / Yearly Savings = Simple Payback
RULES OF THUMB
Simple Payback
Yearly Savings = MMBTU/hr Saved * Yearly hours of Op * Cost of Fuel ($/MMBTU)
Equipment Cost / Yearly Savings = Simple Payback
RFQ Toolbox
September 18, 2018

20. Stoichiometric Combustion Process
RULES OF THUMB
Stoichiometric Combustion Process
This relates to the ratio of natural gas to air for a combustion process.
Standard is 10 parts air to 1 part gas assuming the system DOES NOT run with excess air.
RFQ Toolbox
September 18, 2018

21. Stoichiometric Combustion Process
RULES OF THUMB
Stoichiometric Combustion Process
If you have an exhaust from a gas fired oven and you know the gas usage then you can estimate the stack flow rate for quick energy savings calculations. This only works for 10:1 air to gas ratios. You will have to adjust if it is running with excess air.
RFQ Toolbox
September 18, 2018

22. Stoichiometric Combustion Process
RULES OF THUMB
Stoichiometric Combustion Process
If oven gas usage is 3 MM BTU’s /Hr then this equates to 3000 Ft3/hr of natural standard conditions (1000 BTU/Ft3 for Natural Gas).
Since we are assuming 10:1 air to gas then we know that the combustion air flow will be 30,000 Ft3/hr.
RFQ Toolbox
September 18, 2018

23. Stoichiometric Combustion Process
RULES OF THUMB
Stoichiometric Combustion Process
This gives a total of 33,000 Ft3/hr (SCFH).
Convert to SCFM = SCFH/60
Stack Flow = 33,000/60 = 550 SCFM
RFQ Toolbox
September 18, 2018

24. Questions? 24

25. Thank you! 25