Heat Recovery Equipment Recuperators - General flue gas heat exchanger o Counter flow o Shell and tube o Combination Preheat air prior to combustion Limitation based on the flue gas temperatures o Solution – ceramics Heat Wheels Low to medium to High temperature waste heat Up to 75% efficiency Needs installation of large disk and supporting ducting Heat Pipe Lightweight and compact Virtually no mechanical maintenance 60% to 80% efficiency Used in heating and cooling operations Heat Pump Used to recover low grade waste heat Best when heating and cooling capabilities are used Case Study 1 SunChemical Spray Drying System Heat Recovery employed: Heat Wheel
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Heat Recovery
Equipment
Recuperators - General flue gas heat exchanger
o Counter flowo Shell and tubeo Combination
Preheat air prior to combustion Limitation based on the flue gas temperatures
o Solution – ceramics
Heat Wheels Low to medium to High temperature waste heat Up to 75% efficiency Needs installation of large disk and supporting ducting
Heat Pipe Lightweight and compact Virtually no mechanical maintenance 60% to 80% efficiency Used in heating and cooling operations
Heat Pump Used to recover low grade waste heat Best when heating and cooling capabilities are used
Case Study 1
SunChemicalSpray Drying System
Heat Recovery employed: Heat Wheel
Air Flow: 21,000 CFM
Flue gas Temperature: 203°F
Increased intake temperature ~100°F
Heat Recovered (e=90%)=2.3 Million BTU/Hr approximately $25 dollars and hour
ROI= 1.5 years
Estimated 10 year profit = $1.7 million
Food Processing PlantHeat Recovery employed: Condensing Economizer
original boiler efficiency 86% fuel cost $7.8 per mm Btu average load 8200 hrs/yr at 80%
Application
simple condensing, preheating make-up water 40,000 pph and 60,000 pph (150 psig)
Analysis
installed cost of $680,000 annualized fuel savings of $640,000 simple payback just under 13 months
Case Study 2
MckennaCoated Paper drying system
Heat Recovery process employed: Oven Exhaust to Oven make up air
Oven Exhaust: 5000 SCFM @250
Flue gas Temperature: 250 F
Increased intake temperature ~100°F
Heat Exchanger – Counter Flow plate /Air to air
Heat Recovered (e=65%)=561,000BTU/Hr approximately $9.21dollars and hour
Annual Savings @ 4000 hrs- $63000
Approximate Installed cost- $37000
Payback @2000 hrs- 14-15mnths
Payback @ 4000 hrs- 7-8mnths
Payback @6000 hrs- 5nths
Wegmans Tunnel Oven Heat Recovery Methodology
Heat Energy can be recovered via Ovens
- Directly from the Product - From the Oven Belt- Through Surface Radiation- Exhaust Air System
Heat recovery was done as a process-to-process recovery methodology using exhaust air to heat surroundings.
Assumptions made during analysis
-Exhaust flow rates were assumed based on similar tunnel ovens.
-Tunnel oven operating temperature was assumed by taking the average over a period of time.
-Counter flow plate heat exchangers were utilized.
Heat transfer formula-1.08*CFM*(T2-T1)8*n
n=efficiency of heat exchanger (65%)
T1=Exhaust air temp
T2= air temperature of outside air before passing through heat recovery
Approximate Energy Savings
1 shift -2575hrs $5331.01
2 shifts- 5150 hrs $10662.04
3 shifts- 7725hrs $15993.03
Approximate installation cost- $26000
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