3rd Steinmüller Engineering Conference 2019€¦ · 600MW boiler damaged by a significant...

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3rd Steinmüller Engineering Conference 2019

Replacement of a damaged 600MW boiler:

A review of the design activities and

technical challenges

Speaker : Armin Martz

Co-Speaker : Thomas Will

2

Introduction

The 600MW coal-fired boiler (Main steam design temperature 545°C, design pressure 19.4

MPA) was designed by L&C Steinmueller GmbH in the 1970ies

600MW boiler damaged by a significant over-pressurisation incident in 2014

Require demolition and rebuild of boiler within existing structure

Recovery project has many challenges, this papier focus on:

Demolition activities

Design approach and challenges

Source: publications from ESKOM

3

Contents

Part 1 Part 2

Project Scope

Demolition

HP Pipe Demolition

Structure Assessment

Boiler Demolition

Lessons Learnt

Design Activities

Design Team Setup

Design Approach

Boiler Re-engineering

Lessons Learnt

Conclusion


4

Project Scope


Boiler structure retained

Damaged Plant

Undamaged Plant

Air

Heater

Fabric Filter

Plant

Main Steel

Structure

Boiler

MillsFans

Ducting

HP

Piping

Turbine

Plant

Boiler structure retained

Damaged Plant

Undamaged Plant

5

HP Pipe Demolition

Aux Bay

Turbine Hall

• HP piping followed a cutting and dismantling approach

• Installed blocking frames to minimize pipe movement

(cold pull gradually released)

• Installed temporary restraints and supports for rigging

• Salvaged components capped and preserved


6

Pre-demolition Structural Assessment & Repair

• Condition of structure assessed prior to

demolition

• Visual inspections

• 3D laser surveying

• Structural modelling

• NDT of welds

• Bolt removal & inspection

• Assessment concluded that structure

maintained original load bearing capacity,

only required minor repair.

• Performed temporary repairs prior to

demolition

• Permanent repairs will follow post demolition


7

Boiler Demolition

• Boiler internals

• “cut-and-drop” approach

• Removed bottom ash hopper

• Cut evaporator bottom slope

• Erected “cushion” on 0m level

• Installed demolition curtain from 0-16m

• Used evaporator walls as chute

• Drop test

• Concerns over impact forces transferring to

boiler supports

• Installed strain gauges & performed drop test

• Determined safe cut sizes

• Boiler external equipment & water walls

• Controlled cut, dismantle & rigging


8

Boiler Demolition

“Cushion” at 0m level

Evaporator walls used as chute Windows

cut out in

evaporator

Demolition

curtains

Super heater

bundle

dropped onto

cushion


9

Demolition Challenges & Lessons Learnt

• Demolish boiler in between operating units, may not

impact operation & maintenance of adjacent units

• Reuse of main steel structure require continuous

structural assessment

• Rigging studies develop progressively as areas

become accessible

• Full time resources to review rigging studies while

being developed to limit standing time

• Demolition period: 13 months

• 7600 ton of steel removed from site to date


10

Empty Structure Post-demolition





Part 2

Design Activities

Design Team Setup

Design Approach


Lessons Learnt

Conclusion

12

Design Team Setup


Eskom – Steinmüller Cooperation before project

• Acquisition of IP (manuals, tools)

• Training (classroom, on-the-job)

• Cooperation in various Eskom projects, e.g.

• Coal studies incl. thermodynamic modelling

• Low-NOx retrofit studies & design

• Boiler over-pressurisation root cause analysis and damage assessment

Architect Engineer

Design Authority

Pressure Parts &

Combustion Systems

Steam piping & LPS

Steel Structures

DimBo thermodynamic model

13

Design Approach


• Reuse of the main steel structure resulted in

requirement for “like-for-like” replacement.

• As close to original design as practical

• Maintain boiler load & load distribution

• Designed using TRD (original code) for the

boiler

• Modifications required due to

• Material availability

• Current emissions legislation

• Current fabrication & construction techniques

• Design methodology

• Redraw original drawings

• Compare to site as-built information

• Validate through calculations

• 3D modelling for clash detection

14


Example for design modification data sheet

• A modification register was established and is

managed throughout design process.

• Modifications are evaluated based on

• Technical

• Financial

• Safety

• Environmental

• Operating

• Timing

• Number of modifications per system:


• The only plant changes are related to the

low NOx coal burners

30 Boiler pressure parts 16 Air and flue gas ducts

7 Boiler non-pressure parts 3 Oil and gas burners

7 Boiler process design 4 Coal burners

12 Structural elements

15

Boiler Re-engineering – Pressure Parts


Modification A3 Transition pieces helical wall - vertical

wall

Old design Transition was designed using individual

tube bends

Motivation Easier manufacturing and construction;

minimization of shrinkage and welds

New design Transition designed by forgings (1 helical

tube connects to 6 vertical tubes)

Modification A1 Flat ends of various headers

Old design Flat ends with relief groove

Motivation Negative experiences with this design.

New design regulations no longer allow

for high temperature services.

New design Flat ends without relief groove A1: Old flat

end designA1: New flat

end design

A3: Old transition piece

A3: New transition piece

16

Boiler Re-engineering – Ducting

3D model of air supply system

• 3D CAD model for duct design

• 2D drawings derived from 3D model

and detailed

• Old drawings used as reference

documents

Design modification of flue gas duct

(Attemporation no longer required) Source: publications from ESKOM

17

Boiler Re-engineering – Firing System

• New emissions limit: 750mg/Nm3 (10% O2)

by 2020

• Implementation of low-NOx firing system

• Replace old burners with SM V® Burners

• Burner designed to enable retrofit to remaining units at station

• Arrangement on furnace wall unchanged

• Burner internals incl. mixing elements changed


18

Boiler Re-engineering – PF Piping

• PF routing currently designed as “like-for-like”

• PF distribution not ideal for low-NOx burners

• PF modification proposed:

Dynamic classifier with 4 individual PF pipes


Old design New design

19


• Main steel structure & primary steel

structure

• Repaired & reused

• New boiler loads evaluated in structure

design model

• Minor strengthening required due to new

loads

• Designed primarily using BS

• Secondary steel structure

• Complete replacement within 8 columns of

MSS

• Designed according to SANS

• Design for local material & profile sizes

• BS 4360 Grade 43A replaced with S355JR


20

Boiler Re-engineering – Steam Piping & LPS

• Steam piping (Eskom)

• Main steam, hot reheat, cold reheat,

sootblower piping & drains/vents

• Full detail design

• X20CrMoV 121 replaced with P92

(X10CrWMoVNb9-2)

• P92 results in reduced wall thickness

• Pipe stress analyses performed including

dynamic analyses.

• Higher flexibility required introduction of

additional shock absorbers

• Low Pressure Service (Eskom)

• Compressed air, fire protection, auxiliary

cooling

• Functional design


21

Design Challenges & Lessons Learnt

• Limited availability, accuracy & quality of

original drawings

• Differences between original design and as

built

• Incorporate operational lessons learnt

• Draughting in parallel to design calculations

expedited re-engineering, but calculations

often required drawing revisions

• Design rules well documented in Project

Design Manual

• “Like-for-like” approach agreed up front with

AIA, but still requires regular discussion to

agree on level of design verification and

assurance

• Original plan was to design on a like-for-like

approach. Together with the design

standards, material changes on a damaged

plant it turned out to a very challenging

brown-field project





Speaker : Armin Martz

Co-Speaker : Thomas Will

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