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Muddy Creek WWTP Aeration System Efficiency Upgrade

Metropolitan Sewer District of Greater Cincinnati

June 19 | 2013

Muddy Creek WWTP Aeration System Efficiency Upgrade Brian Mumy, P.E., Brown and Caldwell

Ryan Welsh, P.E., Metropolitan Sewer District of Greater Cincinnati

MSDGC Overview

• Serves the City of Cincinnati and most of Hamilton County

• 7 major treatment plants, 120 pump stations

• 3,000 miles of sanitary and combined sewers

• 184 mgd ADF combined

OWEA Annual Conference | June 19, 2013

Muddy Creek WWTP Overview

• Built in 1958

• 15 mgd Design ADF

• Discharges to Ohio River


Muddy Creek WWTP Secondary Process

• Constructed in 1972

• Two tanks

• 220’x78’x15’ each

• 1.9 MG each

• Plug flow

• Three passes per tank


•Aeration Demand: 6,400 - 13,400 scfm

•Blowers (4)

•Positive Displacement

•200 hp

•Rated at 4,650 scfm each

•Age: Installed in 1972

•Fine Bubble Diffusers

•Sanitaire Ceramic Disc

•Age: Installed in 2008

Prior to Upgrade


• New Blowers with Automatic DO Control

• Contractors: Dugan & Meyers, Lake Erie Electric

• Design Engineers: Brown and Caldwell

• Designed in 2010

• Construction Started in Spring 2011

• Substantial Completion in Spring 2013

• Construction Cost: $7,703,000 *

* Construction contract includes new blowers, diffusers, and automatic DO control at Little Miami WWTP. Muddy Creek construction cost ≈ $2,500,000

Aeration Upgrade Project


• Existing positive displacement blowers were 40 years old

• Decreasing reliability

• Increasing maintenance

• Increasing risk of failure

• Potential for energy savings

Project Motivation


Source: Energy Conservation in Water and Wastewater Facilities,

Manual of Practice No. 32 (WEF, 2009)

Upgrade Evaluation

• Equipment Reliability

• Age of existing equipment

• Capital Costs

• Equipment

• Installation

• Operational Costs

• Maintenance

• Energy



Blower Technologies

• Positive Displacement

• Centrifugal – Single Stage

• Centrifugal – Multistage

• High Speed Turbo

High Speed Turbo Blowers

• Developed in the aerospace industry based on gas turbine engines

• Single stage centrifugal, direct drive

• High speed (15,000-60,000 rpm)

• Air foil bearing

• Blower, motor, VFD, and PLC in single enclosure




Advantages

• High efficiency

• Package design, small footprint, low installation labor

• Lowest maintenance

• Low vibration – isolators not required

• Lowest noise

• Air plenum not required



Disadvantages

• Only for lower flow rates (8,000 to 15,000 scfm max flow per unit)

• VFDs require harmonic filters for protection

• New technology with limited installation base

Business Case Evaluation


Final Alternatives Capital Cost Net Present

Value

1. Positive Displacement Blowers $3,865,000 $7,925,000

2. High Speed Turbo Blowers $2,937,000 $6,096,000

* Replace Blowers – MSDGC Useful Life of Capital Assets Report

* 30 Year Analysis, Electricity Cost $0.073 KW/HR

* MSDGC NPV analysis

High Speed Turbo Blowers Selected

• Lower Capital Cost

• Lower O&M Cost

• Lower Energy Cost

• Lower NPV

• Four High-Speed Turbo Blowers

• HP: 250

• Rated Capacity: 4,770 scfm

• Harmonic Filters

• Electrically Actuated

Butterfly Air Control

Valves

• Startup Date: February, 2012

Equipment Installed


• Each Blower was provided as a package by the manufacturer

• A Master Control Panel (MCP) was also provided by the manufacturer to act as a pressure controller.

• New Dissolved Oxygen Meters

• New Air Flow Meters

Controls Installed


• Luminescent technology

• No membranes or solutions

• Factory calibrated

Dissolved Oxygen Probes


• Thermal Mass Flow technology

• Flow conditioner upstream

• Low pressure loss

Air Flow Meters


Overview of Secondary Aeration


AERATION TANK 1

PASS 1

PASS 2

PASS 3

PASS 1

PASS 2

PASS 3

AERATION TANK 2

BLOWERS

AIR MODULATING

VALVES

AIR FLOW

METERS

D.O. MEASUREMENT

Most Open Valve (MOV) Pressure Control


M

PIT

MOV %

SETPOINT

AIR HEADER

PLC

PID

SPEED % - + -

DRIVE

PLC

MOV

LOGIC

PRESS

SP

AIR VALVE

POSITIONS

M

AIT

D.O.

SETPOINT

PLC

PID

% OPEN - + -

DISSOLVED OXYGEN

PLC

PID

FIT

- + -

FLOW

SETPOINT

FLOW

% OPEN TO MOV

CONTROLLER

PRESSURE

Blower Operation – Communications


Aeration

Master PLC

Blower MCP Master Control

Panel

Blower 1

PLC

• 6 PLCs are inter-connected with Ethernet

• Each Blower PLC and the MCP have PanelView

touch-screens

Blower 2

PLC

Blower 3

PLC

Blower 4

PLC

Pressure Set-point

Blower Operation – MCP Pressure Controls


• The MCP is programmed to

maintain header pressure

by adjusting the blower

speeds.

• MCP determines:

• Which blower is lead

• Time delays for

starting/stopping

• Which pressure

transmitter to use for

feedback

• Dead-bands

Blower Operation – Local Controls


• Blower is normally controlled

from the MCP via Ethernet.

• It can be placed in Local

Control to manually

start/stop and adjust speed.

• Displays speed, pressure,

estimated flow, temperature,

etc.

• Indicates when filter

changes are required based

on pressure differential

Aeration System – HMI Controls


Trending

Blower Details

Overview

Pop-Ups

Energy Savings - Estimated


• Original Positive Displacement Blowers

• Estimated usage of 270 kW

• High Speed Turbo Blowers

• Estimated usage of 212 kW

• Estimated Energy Savings

• $3,000/mo

• $36,000/yr

• ≈ 20%

Actual Energy Savings – First Year


$0

$5,000

$10,000

$15,000

$20,000

$25,000

Ae

rati

on

Bu

ild

ing M

on

thly

Po

we

r C

osts

Month

2009-2011

2012-2013

Average Energy

Savings:

≈ 40%

Actual Energy Savings – First Year


• Average Annual Energy Cost 2009-2011

• $220,000

• Average Annual Energy Cost 2012

• $135,000

• Energy Savings

• $85,000/yr

• ≈ 40%

Lessons Learned


• New Technology

• New manufacturers

• Purchase extended warranty

• Base bid manufacturer

• Performance Testing is Critical

• ASME Performance Test Codes

• PTC-10 – Compressors and Exhausters

• PTC-13 – Blowers – under development

Lessons Learned


• Turndown

• Be weary of manufacturer claims

• Blower controls protect against surge – reduces operating range

• Muddy Creek HMI programming was modified to avoid LCP warnings and keep blow-off valves from opening

Lessons Learned


• Programming System Controls is Critical

• Controls can contribute to energy savings as much as the blowers

• Startup adjustments will be necessary - flexibility in programming is required

• Muddy Creek HMI control was modified to maintain mixing airflow

Questions


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