chpwkshop 20050302 maximizing heat recovery carson

8/3/2019 ChpWkshop 20050302 Maximizing Heat Recovery Carson

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Condensing Economizer

TechnologyBill Carson

Direct Contact Inc.

Direct Contact, Inc. 2003

WASTE HEAT TO POWER WORKSHOP


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Condensing Economizer Provides

New Heat Recovery Opportunities

Very High Heat Transfer Coefficient

Extremely High Heat Transfer SurfaceArea

Low Gas Side Pressure Drops



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WASTE HEAT RECOVERYADDING UP TO MORE THAN A DROP IN THE BUCKET.


DCI-Heat Recovery Vessels

A single chamber vessel is used forclean gases combining adiabatic cooling

and heat recovery in single chamber A dual chamber vessel is designed for dirty

gases: conditioning and adiabatically cooler inits lower chamber and recovering heat in its

upper chamber.


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Heat Content of Flue Gas

The heat exhausted from a boiler isdependent on two factors:

Flue Gas Temperature (boiler specific) Water Vapor Content (humidity)

The excess combustion air and type of fuelburned determines the amount of watervapor (humidity) in the flue gas.

hydrogen combustion generates only water vapor pure carbon combustion generates no water vapor Among hydrocarbons, methane combustion generates the most

water vapor


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Combustion Stoichiometery

Hydrogen moles O2 (G) + 2 H2 (G) 2 H2O (G)

mass 32.00 + 4.03 36.03

Carbon moles O2 (G) + C (S) CO2 (G)

mass 32.00 + 12.01 44.01

Methane moles O2 (G) + CH4 (G) CO2 (G) + H2O (G)

mass 32.00 + 8.02 22.01 + 18.02

Ethane moles O2 (G) +2/7 C2H6 (G)

4/7 CO2 (G) +4/7

H2O (G)

mass 32.00 + 8.59 25.15 + 15.44

(Basis = One Mole of Oxygen)


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Combustion Energy

FUEL

Higher Heat

Value (BTU)

Lower Heat

Value (BTU)

Latent Heat

Water (BTU)

Heat Content In

Water Vapor

Exhausted(Part of Total)

HYDROGEN 246335 208143.9 38191.1 15.50%

CARBON 169256.9 169256.9 0 0.00%

METHANE 191475.5 172389.9 19087.6 9.97%

ETHANE 191475.5 175419.7 16336.7 8.55%


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Psychometric Chart


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Simplified System


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Nomenclature

Mass Heat Direction Description

WMW QMW in Boiler Make Up Water

WDAV QDAV out Deaerating Air Vent

WBD QBD out Boiler Blow Down

WFG QFG out Boiler Flue Gas--- QBRH out Boiler Radiant & Convective Heat Loss

WCA QCA in Combustion Air

WNG QNG in Natural Gas

--- QSRH out Steam Distribution Radiant & Convective Heat Loss

WDWC

QDWC

out Drip Waste Condensate

--- QPL out Process Heat Load (Client Heat)

WWC QWC out Waste Condensate

--- QCOMB generated Heat of Combustion

WASTE HEAT RECOVERY


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Mass and Energy Balance

OVERALL ENERGY BALANCE

(QMW + QCA + QNG)IN + (QCOMB)GEN = (QDAV + QBD + QFG+ QBRH+ QSRH+ QDWC+ QPL+ QWC)OUT

OVERALL MASS BALANCE

(WMW + WCA + WNG)IN = (WDAV + WBD + WFG+ WBRH+ WSRH+ WDWC+ WPL+ WWC)OUT

SYSTEM EFFICIENCYeff = QPL/[QCOMB + (QMW + QCA + QNG)IN]

WASTE HEAT RECOVERY


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Heat Flow

WASTE HEAT RECOVERY


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Captured Heat can be returned to the Boiler system by

1. Heating combustion air

2. Heating water make-up

Todays discussion focuses on the latter and we will examine

1. The heat removed above the Dew Point (via an Economizer)

2. The heat removed below the Dew Point temperature (via a

Condensing Economizer)

Heat Return Paths

WASTE HEAT RECOVERY


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Flue Gas Heat Recovery

WASTE HEAT RECOVERY


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Assumptions Used in Mass and

Energy Balance Boiler produces 6,000 pounds per hour of steam at 100-psig saturated Combustion air, fuel and makeup water are all at inlet temperature 60F

Combustion air dew point is at a temperature of 40oF

Fuel is 100% methane, combustion air is 10% excess, and the combustion efficiency is 100%

The boiler has 0% blow down and negligible heat is lost from the deaerating heater vent

The boilers radiant and convective heat losses are at 2% and no heat is lost from the distribution piping

Inefficiencies of rotating equipment are negligible

Flue gas enters economizer at 530oF and leaves the economizer at 320oF

51% flue gas passes through the condensing economizer leaving at 113oF

The condensing economizer gas exhaust and hot flue gas, directly from the economizer,combine to produce a stack exhaust temperature of 219.2oF

WASTE HEAT RECOVERY


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Heat AvailableTotal Heat in Flue Gas leaving Boiler

1,742,160 BTU/hr100%

Heat captured in the Economizer

428,240 BTU/hr24.6%

Heat captured in the CondensingEconomizer

390,000 BTU/hr(Additional 22.4%)

Condensing Economizer Only

444,000 BTU/hr25.5%

WASTE HEAT RECOVERY


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ADDING UP TO MORE THAN A DROP IN THE BUCKET.


DCI Heat

Recovery Vessel

Note two chambers

ConditioningChamber

Heat RecoveryChamber

Heat Recovery

Chamber

Conditioning

Chamber

WASTE HEAT RECOVERY


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Conditioning Chamber

Incoming gas is flash cooled

- Water vapor is evaporated

- Gas is cooled and humidified- Temperature of gas is driven to

saturation (Wet Bulb)

Large particulate is captured in excesswater

Majority of liquid water is separatedfrom gas stream

WASTE HEAT RECOVERY


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Heat Transfer Chamber

Saturated gas enters thischamber and is contacted witha large number of smalldroplets.

The gas is cooled to below itsinlet dew point temperature,condensing all the water usedto adiabatically cool it in the

conditioning chamber, as wellas some of the water vapor inthe pre-quenched gas .


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Low Grade Heat

A Heat Repository (or Heat Sink) isrequired to cool exhaust gas.

Finding a home for the hot water you createcan be challenging

but if you can use this heat, and replacevirgin energy, the project can turn into a netmoney maker.

Good Examples: Boiler Feed Water,Domestic Hot Water, Process/Wash Water


WASTE HEAT RECOVERYADDING UP TO MORE THAN A DROP IN THE BUCKET


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Direct Contact Inc.Heat Recovery System

~14 MBTU/hr saved >9 million gallons/yr.

water was recovered >9,000 tons/yr. less

CO2 was generated

Average fuel savings>$2000/day

< 2-yr payback

Seattle Steam Company



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CO2 was generated


< 2-yr payback

Pactiv Corporation



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CO2 was generated


< 2-yr payback

James Hardie Gypsum; now BPB



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1st Unit of this designwas installed in 1985

and is still performing 2nd unit was installed at

the same mill in 1991

3rd system has beeninstalled on a Hog FuelBoiler Exhaust and iscapturing >25 MBTU/hr

Northwest Groundwood Refiner



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G U O O O UC


Direct Contact Inc.Hog Fuel Boiler

DAISHOWA AMERICA

Installed 2002

~30 MBTU/hrthermal heat saved

Average fuel

savings >$150/hr



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Why lose all

Consider a

Heat Recovery System

this heat?

chpwkshop 20050302 maximizing heat recovery carson

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