Removing Salt From Coal Mine Wastewater in a Remote, … · Removing Salt From Coal Mine Wastewater in a Remote, Wet ... • Draft-tube reactor design ... • Concentric falling film

Removing Salt From Coal Mine Wastewater in a Remote, Wet Area: Full Scale Experience

Srikanth Muddasani, P.E. Veolia Water Technologies, USA

• Centralized ZLW treatment facility to handle water from six mine locations

• All six mines located within Monongahela River Basin

• Regulatory driver = Chlorides to < 218 mg/L

• Solid wastes generated are disposed in on-site landfill

• Treated effluent is discharged to creek and/or used as frac water

Project Background

2

Contributing Mine Locations

18” Force Main collects water from 4 mines to the North

14” Force Main collects water from 2 mines to the South

CENTRALIZED TREATMENT FACILITY

• Centralized ZLW treatment facility is designed to treat 5 MGD (795 m3/h) of mine water

• Mine water, pretreated for metals removal where needed, conveyed from six source points to the facility through 32 miles of pipeline

• Executed through a Design-Build-Operate contract with Veolia

• June 2010 - Request for proposals issued

• April 2011 - Project awarded

• July 2011 - Construction began

• May 2013 - Full operation

The Project

4

Note 1: Average Value based on the data collected between Jun 1st 2014 to Dec 31st 2014 Note 2: Average Value based on the data collected between Aug 20th,2014 to Sep 5th, 2014

Design Basis - Influent Mine Water

5

Parameters Original Design Current Design1

Design Flow, gpm 3500 (795 m3/h) 2026 (460 m3/h)

pH, S.U. 5 - 10 7.39

Temperature, deg F 38 – 85 (3 – 30 deg C) 60 – 72 (15-22 deg C)

Calcium, mg/L 300 217

Magnesium, mg/L 200 104

Iron, mg/L 150 0.27

Manganese, mg/L 2 0.27

Alkalinity, mg/L CaCO3 700 - 1200 891

Sulfate, mg/L 5,500 2700 2

Chloride, mg/L 1,500 1530 2

TDS, mg/L 10,000 8600

Silica, mg/L as SiO2 10 10

Note 1: Applied to product water prior to remineralization

Effluent Water Quality Requirements

6

Parameters Maximum Effluent Concentration

Chlorides, mg/L < 218

TDS, mg/L < 150 1

pH, S.U. 6 to 9

Minimum Hardness, mg/l as CaCO3 ≥ 50

• Raw Water Pretreatment System

• Reverse Osmosis System

• Thermal Brine Management System

The Process: Three Primary Components

7

Process Overview

8

Primary Objectives 1. Remove TDS and Chlorides 2. Zero Liquid Waste

Facility Overview

9

Evaporator

Crystallizer

RO Trains

Raw Water Tank

Multimedia Filters Lime & Soda Ash Silos

Softening System

1st Stage Clarifier

Dewatering Building

• Multi-stage process

• Two aeration tanks for precipitation of metals such as manganese and iron

• Crystallization tank for removal of alkalinity and hardness

• Draft-tube reactor design

• Solids recycle

• Reduce chemical consumption

• Enhance particle growth and settling characteristics

• Conventional circular clarifier design

Chemical Softening System

10

• Removes residual suspended solids in the effluent from upstream clarification and aluminum precipitation processes

• Backwash water is returned to the Raw Water Feed Tank

• Filtrate is conveyed to the RO System

Multimedia Filter System

11

Reverse Osmosis System

• RO Feed Tank, followed by Cartridge Filtration

• RO Skids designed to achieve chloride and TDS specifications while operating at a high recovery rate

• Five parallel skids, each sized to handle 25% of the design flow, 1 standby

• Thirty-one pressure vessels per skid, each with seven seawater RO membrane elements

• Permeate flows to Product Water Tank, which also collects distillate from Brine Management System

• Prior to discharge, the Product Water Tank effluent is re-mineralized using carbon dioxide and lime water, to protect aquatic life

• Discharged to creek, or to a truck loading station for reuse in energy-related operations.

• Reject is sent to the thermal Brine Management System

The Process Flow - RO System

12

Evaporator

• Concentric falling film unit is divided into two sections with a low concentration side and a high concentration side

• Split design to reduce overall power consumption by allowing a portion of the evaporation to occur at a lower boiling point rise than the final concentration

• Evaporator operates as a Mechanical Vapor Recompression System

• Recycle of hot vapor in the system; minimize auxiliary steam

• Distillates from the Evaporator and Crystallizer are pumped through a Feed Preheater for heat transfer to the incoming brine

• Heat exchanger for efficient energy utilization

Evaporation

13

• Crystallizer includes a vapor body, recirculation pump, and forces circulation heat exchanger

• Vapors created by concentrating the slurry in the Crystallizer are recompressed and recirculated through the heater

• As the brine concentration increases, the solution becomes supersaturated and salts precipitate, resulting in a brine slurry

• A slip stream of the crystallizer slurry is sent to centrifuges for dewatering

• The result: Zero Liquid Waste

• Dewatered salt cake is disposed in the on-site landfill along with the dewatered sludge from the softening processes

Crystallization

14

Thermal Brine Management System

15

Crystallizer Evaporator Heat Exchanger

Distillate Tank

Crystallizer

• Dewatered Salt and Softening Sludge is brought separately to onsite landfill

• Dewatered Salt contains approximately 90 – 95% in solids concentration and Sludge contains 50 – 65% in solids concentration.

• Both passes paint filter press test

• Both Salt and Sludge are mixed before applied to landfill

• Lechate generated in landfill is collected in storage tank and metered back to thermal system

Land fill

16

• Chemical Storage and Feed Systems

• Lime Water Preparation System

• RO Membrane Clean-in-Place System

• Compressed Air System

• Electrical and Control Rooms

• Laboratory

• Communications Equipment

• Maintenance and Storage Areas

• Personnel Amenities

Ancillary Support Systems

17

Feed Water Conductivity

18

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

06/01/14 07/06/14 09/16/14 10/21/14 11/25/14 12/31/14

Cond

uctiv

ity (µ

s/cm

)

Days

Current Feed Conductivity Design Feed Conductivity

Original Design Conductivity = 13,000 µs/cm Current Avg Conductivity = 11,180 µs/cm

Product Water Conductivity

19

Product water Cond before Remineralization = 63 µs/cm Final Effluent Discharge Cond = 142 µs/cm

0

20

40

60

80

100

120

140

160

180

200

06/01/14 07/06/14 09/16/14 10/21/14 11/25/14 12/31/14

Cond

uctiv

ity (µ

s/cm

)

Days

Product Water Cond before Remin Final Eff Discharge Cond

Feed Water Chlorides

20

1400

1450

1500

1550

1600

1650

8/20/14 8/22/14 8/26/14 8/28/14 9/1/14 9/2/14 9/3/14 9/4/14 9/5/14

Chlo

rides

(mg/

L)

Days

Current Feed Chlorides

Current Avg Feed Chlorides = 1,530 mg/l

Final Effluent Chlorides

21

0.00

5.00

10.00

15.00

20.00

25.00

1/1/2014 1/21/2014 2/10/2014 3/2/2014 3/22/2014 4/11/2014 5/1/2014 5/21/2014 6/10/2014

Efflu

ent C

hlor

ides

, mg/

l

Days

Final Effluent Chlorides = 16 mg/l

Please Note: Waste Estimation for design condition was estimated based on 3500 gpm flow Waste Estimation for Current Average Condition was estimated based on 2026 gpm flow

Estimated Waste Generation

22

Waste Design Condition Current Average Condition

Softening Sludge (on a 100% dry basis) 6,666 lb/hr (3,030 kg/hr) 2,200 lb/hr (1,000 kg/hr)

Salt (on a 100% dry basis) 17,500 lb/hr (7,954 kg/hr) 8,710 lb/hr (3,960 kg/hr)

Total Waste Generated (on 100% dry basis) 24,166 lb/hr (10,984 kg/hr) 10,910 lb/hr (4,960 kg/hr)

• Treatment process achieves > 99% removal of chlorides using state-of-the-art membrane technology

• Energy efficient evaporation and crystallization technology for brine management

• Solid waste generated onsite is disposed into onsite landfill and leachate generated at the landfill is sent back to the facility’s thermal treatment process

• Since no liquid waste leaves the property, this facility is termed as a “zero liquid waste” (ZLW) facility

Summary

23

Thank You!