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