People. Ideas. Innovation.

Reduction of Natural Gas Usagefor City of Corvallis Waste Water Facility

Kendra Seniow, Melissa Ghiglieri, Kelly WilsonSponsor: Mr. Keith Turner , P.E. Advisor: Dr. Christine Kelly

Chemical, Biological, Environmental Engineering

Issue StatementThe chemical building ventilation heating system relies on the combustion of natural gas as the building is not connected to the waste water facility hot water loop.

Project ScopeThe purpose of this project is to review the chemical building glycol heat recovery system and other options for decreasing methane utilization in the Chemical Building including connection of the building to the hot water loop.

Methodology1.Characterize heat recovery system in terms of the overall heat exchange coefficient, U.

• Measure temperature rise over heat exchangers of air and glycol lines

• Measure glycol concentration in glycol line

Results

, ( )Furnace AIR P AIR Furnace OutsideAirQ m C T T

, ( )HX AIR P AIR HX OutsideAir lmQ m C T T UA T

saved furnace HXQ Q Q

Assumption #1: TGlycol is constant ~45oF

Assumption #2: ΔTlm=TGlycol-THX Air

2. Develop theoretical model to combine with empirically determined U value to estimate savings provided by heat recovery system.

3. Use historical temperature data to predict natural gas needs of building and compare with actual natural gas used to estimate heat recovery system effectiveness.

Natural Gas (methane) Demand

Water is disinfected with chlorine (sodium hypochlorite) which is then removed by sodium bisulfite. These chemicals are stored in large tanks in the chemical storage building (Figure 1). Due to the risk associated with inhalation of these chemicals, the storage building air is required to be replaced 12 times per hour. This high ventilation rate necessitates high levels of natural gas to maintain building temperature at 55ºF(Figure 2).

Figure 1. Corvallis Waste Water Reclamation Plant.

Waste Water Plant Overview

Methane Production

The processing of wastewater solids in an anaerobic digester results in the production of methane, which is burned in a hot water boiler. This hot water loop (Figure 1) both maintains the digester temperature and heats the facility offices. Excess methane is burned in a waste gas flare and an alternative application is sought.

Glycol Heat Recovery System

In 2004, a heat exchanger system was installed in the chemical storage building to conserve building heat and lessen the natural gas requirement. An ethylene glycol loop (Figure 7) captures heat from out-going air and then preheats incoming air. From information in Figure 2, it is not immediately clear that the glycol loop has the intended impact.

Figure 2. Daily Natural Gas Usage by the Chemical Building Air Exchange System (Averaged Monthly)

Glycol Heat Recovery System Installed

(July 2004)

The savings in natural gas expenditures provided by the heat recovery system were estimated using the model from Methodology 1 and 2 (Table 1, column 1-Theoretical Savings) as well as by using temperature and natural gas records from methodology 3 (column 2- Theoretical Expenditures).

Actual Natural Gas Expenditures **

Theoretical Expenditures of

HVAC without Heat Recovery System

Theoretical Savings due to Heat Recovery

System

Daily (April 14, 2010) $8.22/day $22.48/day $5.42/day

Annual (2009) $5,300/year $5,700/year $1,620/year

Maximum Daily Temperature < 55oF (average 2001-2010)*

108 days/year --- ---

Table 1. Estimated Glycol Heat Recovery Performance for Natural Gas Use Reduction. The difference between the theoretical expenditures of the HVAC without Heat Recovery System and the Actual Natural Gas Expenditures should approximate our models’ predicted theoretical savings due to the heat recovery system.

*Historical temperature data was obtained from NOAA website.**Natural gas usage by the chemical storage building since 2001 was provided by the City of Corvallis WWRP.

Figure 8. Estimated Daily Reduction in Natural Gas Expenditures Based on Theoretical Model.

Figure 9. Estimated Daily Reduction in Natural Gas Expenditures Based on Historical Data.

Hot Water Loop Extension : Cost Benefit

Figure 3. Pre-Heater Heat Exchanger with Temperature Reading Locations Indicated.

Figure 5. Theoretical Savings by Glycol Heat Recovery System.

Figure 4. Heat Recover System.

Figures 8 and 9 show the comparison between the reduction of natural gas expenditures using the developed theoretical model versus the historical natural gas use data provided by the City of Corvallis WWRP.

Estimated Capital Cost of Extension

Theoretical Annual

Savings ($/yr)

Simple Payback

Period (yr)

Extension Option A

$15,900 $5,900 2.8

Extension Option B

$7,300 $5,900 1.3

Willamette River

Exist

ing H

ot Wat

er L

oop

Proposed Hot W

ater Extension

Figure 9. Hot Water Loop Extension Options.

Figure 9 and Table 2 include the cost benefit information for extending the hot water loop to the chemical storage building and re-plumbing the glycol loop furnace pre-heater heat exchanger with the hot water. Table 2. Estimated capital costs and savings associated with extending the hot water loop to the chemical storage building.

Figure 7. Schematic of the Chemical Storage Building piping and ventilation system; the preheating heat exchanger is located before the furnace in the HVAC room. Two thermostats, located on the northern side of the building, ensure that the building set-point is maintained at 55˚F.