Western BLRBAC Review/Refresher of Tappi Water Quality Guidelines and Contamination Procedures for mill boilers operating on high purity water

Transcription

1 Western BLRBAC Review/Refresher of Tappi Water Quality Guidelines and Contamination Procedures for mill boilers operating on high purity water October 29, 2014 Commitment makes the best chemistry. 1

2 TAPPI Documents TIPP reaffirmed 2011 Water quality and monitoring requirements for paper mill boilers operating with high purity water Scope: feedwater, boilers and steam purity continuous and manual sampling points and sampling methods Control limits: total hardness, ph, conductivity, silica, sodium, oxygen, iron and copper, TOC, alkalinity/ph/phosphate for congruent phosphate

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4 ASME Guiding Principles

5 Boiler Water - Congruent Phosphate Control

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7 TAPPI Documents TIPP issued 2000 Response to contamination of high purity boiler feedwater Boiler ph High Boiler ph Low Boiler contaminated with Black Liquor Boiler Silica Feedwater Total Hardness Feed water Iron

8 Response Criteria and Time Line Response Time Boiler ph HIGH (Black Liquor same at high conc.) Slight: ph - > 0.2 above normal - 48 hours Moderate: ph 10.5 to hours Severe: ph >11-8 hours Boiler ph LOW Slight: ph - > 0.2 below normal hours Moderate: ph 8.0 to hours Severe: ph hours Severe: ph < immediate Monitor Foaming in all of above Sodium limit ppb

9 Response Criteria and Time Line Response Time Boiler Silica Slight: 120 % upper limit - few days Moderate: % upper limit days Severe: > 140% upper limit - 8 hours Feedwater Hardness (refer to ph LOW) Slight: < 2 ppm - couple days Moderate: 2 ppm - 24 hours Severe: > 5 ppm - 12 hours Feedwater Iron Slight: < 100 ppb - couple days Moderate: 100 ppb - 24 hours Severe: > 300 ppb - 12 hours

10 Issue High Purity Water is relatively unbuffered Buffer A buffer is a substance that accepts either hydrogen (acids) or hydroxyl ions (bases, caustic) minimizing ph changes. For example, the bicarbonate ion buffers the ph of sodium zeolite make up to boilers Most mill boilers operate at pressures above 600 psig and require high purity water in order to maintain the control limits of a congruent phosphate boiler water program Typically the make-up is produced by demineralization and/ reverse osmosis Many mills have condensate polishers on the sodium or amine cycle

11 Oxygen Pitting - Economizer By deaeration and adding a chemical oxygen scavenger dissolve oxygen limit is 0 to 5 ppb 11

12 Total Hardness Scale - Overheating Fireside Waterside Fireside Waterside 454 C Scale 316 C Tube Wall Tube Wall 260 C 260 C Without Scale With Scale

13 Attack on Steel

14 Concentrating Mechanism Porous Iron and Copper Deposits

15 Universal Truth safety, medicine, aviation, etc. PREVENTION Proper design and operation can prevent all incidents DETECTION Sampling and monitoring the critical variables is essential RESPONSE Standard Operating Practices, SOPs, DCS controls Training Generally - more than 1 thing has to go wrong

16 Demineralized Make Up Subject to acid, caustic, salt and amine ingress Prevention (with redundancies) Block valve on regenerant lines and vessel outlet Auto valve positioners and permissive starts SOPs for regeneration procedure and regen logs Detection (with redundancies) Automatic instrumentation; conductivity, ph, sodium, silica as recommended by TAPPI Multiple alarms set points with bypass and shut-downs controls Coordinated instrument checks and maintenance Response Excursion Procedures Excursion Training

17 Condensate Returns Subject to contamination from black liquor, hardness, caustic, acid, polisher regenerants, sulphite etc. Prevention (with redundancies) Locating all potential sources Back-flow devices, lock-out and start-up SOPs etc. Condensate dump systems Detection (with redundancies) Automatic instrumentation; conductivity, sodium, calcium Proper alarms and condensate dump limits Scheduled instrumentation maintenance and dump system checks Response Excursion Procedures Excursion Training

18 Severe Contamination - 3 Case Studies Response time for slight and moderate ingress of acid, caustic and black liquor is in hours Response time for severe ingress of acid, caustic, and black liquor is: Minutes to stop attemperating water and reduce load Faster than information can gained from boiler ph some time lag Highly dependent on ph and conductivity information from demin storage, condensate receive and feedwater Additional information from sodium and cation conductivity is useful

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20 # 1,2,3 SOP Action # 2 caustic ingress into a unit in service # 1 acid backup into dilution water

21 Case Study No. 1 Regenerant Acid Ingress Incident Concentrated acid from HP acid pumps backed up through the dilution water sourced at the demin tank outlet Acid ingress in feedwater into the steam drum and 5 % attemperating water Prevention GAP No check valve in the dilution water line Questionable location as source of dilution water Detection GAP Conductivity probe located at the inlet to the demin tank could not detect outlet contamination Conductivity on the deaerator had no high alarm set point Response GAP Boiler water reached a ph of 4.5 Attemperating water not turned off

22 Case Study No.1 Damage ruptured pendant SH tubes due to plugging Inhibited HCl cleaning of the boiler to remove iron corrosion products Hydroxyacetic/formic cleaning of the superheaters to dissolve plugs of corrosion products and sloughed off magnetite. Safe for austenitic SH steel and high iron chelation properties

23 Case Study No.1 Corrective Action Installed a check valve in the dilution water line Added a conductivity sensor after the dilution water take-off that shut off the demin storage tank pumps at 25 mmhos Eventually changed to decationized water for dilution water Modified SOP for action at 25 mmhos in the feedwater to shut off the attemperating water

24 Case Study No. 2 Regenerant Caustic Ingress Incident 4% caustic diluted regenerant intended to regenerate B SBA crossed over to A SBA that was in service Caustic ingress at the steam drum resulting in foaming and contamination of 5 % attemperating water Prevention GAP manual valve left open on the regenerant line to A SBA Minimal demin water storage volume and time Detection GAP No conductivity probe in the combined SBR outlet no high alarm set point conductivity in feedwater Response GAP Boiler water ph of 11 plus with considerable foaming Attemperating water not turned off

25 Case Study No.2 Damage Shadow Shots ruptured pendant SH tubes due to plugging Inhibited HCl cleaning of the boiler to remove iron corrosion products and magnetite Hydroxyacetic/formic cleaning of the superheaters to dissolve plugs of corrosion products and sloughed off magnetite. Safe for austenitic SH steel and high iron chelation properties Location of plugged tubes Is unpredictable

26 Case Study No. 2 Corrective Action Installed a double block and bleed on all acid and caustic regenerant inlets Installed automatic valve positioner on the regenerant inlet with permissive start Added a conductivity sensor after each anion that would automatically put the unit in rinse at 25 mmohs conductivity Wrote an SOP for action at 25 mmhos in the feedwater to shut off the attemperating water

27 Case Study No. 3 Black liquor ingress Incident Large amount of black liquor contaminated digester condensate Caustic ingress at the steam drum resulting in foaming and contaminating - 20 % attemperating water Prevention GAP No redundancy in conductivity dump system Frequent black liquor leaks into the condensate Detection GAP Single conductivity sensor was not working straight line recording Response GAP Appreciation of the impact of 20% attemperating Attemperating water not turned off

28 Case Study No.3 - Damage ruptured pendant SH tubes due to plugging Inhibited HCl cleaning of the boiler to remove iron corrosion products and old hardness scale Hydroxyacetic/formic cleaning of the superheaters to dissolve plugs of corrosion products and sloughed off magnetite. Safe for austenitic SH steel and high iron chelation properties

29 Case Study No. 2 Corrective Action Isolate the attemperating water from the condensate Install a mixed bed polisher on the make-up to the attemperating water Added a separate deaerator for the attemperating water 20 % Typically the failure is on on the hotter outlet of the pendant

30 Lessons Learned and Best Practices Demineralized Make Up Subject to acid, caustic, salt and amine ingress Prevention (with redundancies) Manual and auto valves on regenerant lines and vessel outlet (double block and bleed preferred) Auto valve position indicators and permissive starts in DCS Check valve on the dilution water SOPs for regeneration procedure with regen logs Regular PMs on all valves and instruments Shared coordination between operations and instrument department Scheduled audits Reporting and review of all near miss incidents Design in redundancies

31 Lessons Learned and Best Practices Demineralized Make Up Detection (with redundancies) Automatic instrumentation; conductivity, ph, sodium, silica as recommended by TAPPI Multiple alarms set points with bypass and shut-downs controls in the DCS. Typically alarms are set for regeneration purposes not for contamination Scheduled operator checks of instruments and recording results Response Written excursion SOPs jointly developed by water consultants, senior mill supervisors and operators and approved by mill management Excursion training annually

32 Lessons Learned and Best Practices Condensate Returns Subject to contamination from black liquor, hardness, caustic, acid, polisher regenerants, sulphite etc. Prevention (with redundancies) Locate all potential contamination sources Install back-flow devices on live stream injections Develop lock-out and start-up SOPs including dumping until clear e.g. machine condensate that has a high potential for iron and copper on start up Redundancies on critical potential contamination Include local dump stations and dump stations at the central condensate receiver Duplicate conductivity cells at central condensate receiver External cooled conductivity probes are preferred to inline probes because they are easier to verify

33 Lessons Learned and Best Practices Condensate Returns Detection (with redundancies) Automatic instrumentation; conductivity as a minimum Make better use of sodium sensors - will detect black liquor, raw water, carryover Multiple alarms set points, dumps and shut-down controls in the DCS Regular scheduled operator checks of instruments and recording results Response Written Excursion SOPs jointly developed by water consultants and senior operators and approved by management Excursion training annually

34 Lessons Learned and Best Practices Boiler Feedwater Prevention Last line of defense against contamination Severe contamination Detection normally leads to reduced loads or shut-down of boilers of attemperating water can lead to costly damage to the superheaters Conductivity, ph sensors are a a minimum (also on boiler) Ability to connect to a sodium sensors sequencing Easy access to manual samples to verify continuous sensors Rapid Response Management approved SOPs with limits for conductivity and ph that would initiate stopping the attemperating water, load reduction and boiler shutdown

35 Questions, Comments and Suggestions