NB/T 11512-2024Code for chimney design of fossil-fired power plant (English PDF)

Foreword

This document was issued on 24 May 2024 by the National Energy Administration of the PRC and takes effect on 24 November 2024.

It is a NB/T standard: recommended rather than compulsory, but it is the text a Chinese reviewer applies when assessing a submission.

It is classified under ICS 27.100, Chinese classification P 60.

This standard was prepared in accordance with the requirements of the Notice of the General Department of the National Energy Administration on issuing the 2019 plan for the formulation and revision of industry standards in the energy field and the plan for the translation and publication of English versions, document Guo Neng Zong Tong Ke Ji [2019] No. 58. The drafting group carried out extensive engineering investigation and special research, summarised the practical experience of chimney design in fossil-fired power plants, referred to the relevant standards in China and abroad, and prepared this standard on the basis of thorough analysis, research, discussion and wide consultation.

The main technical content of this standard is: general provisions; terms; basic requirements; chimney type selection and anticorrosion scheme; actions and combinations of actions; single tube chimneys; single liner and multi-liner chimneys; steel chimneys; chimney foundations; chimney ancillary facilities; and chimney renovation.

This standard is administered by the National Energy Administration, was proposed by the Electric Power Planning and Engineering Institute, and is under the routine administration of the Power Generation Design Standardization Committee of the Energy Industry. The Electric Power Planning and Engineering Institute Co., Ltd. and China Power Engineering Consulting Group Northwest Electric Power Design Institute Co., Ltd. are responsible for the interpretation of the specific technical content.

Chief drafting organizations of this standard: Electric Power Planning and Engineering Institute Co., Ltd.; China Power Engineering Consulting Group Northwest Electric Power Design Institute Co., Ltd.

Participating drafting organizations of this standard include China Power Engineering Consulting Group Northeast Electric Power Design Institute Co., Ltd.; China Power Engineering Consulting Group Central Southern Electric Power Design Institute Co., Ltd.; China Power Engineering Consulting Group East China Electric Power Design Institute Co., Ltd.; and China Power Engineering Consulting Group Southwest Electric Power Design Institute Co., Ltd.

1 Scope

NB/T 11512-2024 is the Chinese code for designing the chimney of a fossil-fired power plant, and for renovating an existing one. It exists because flue gas desulphurisation changed the chimney from a hot dry structure into a cold wet one, and in doing so turned a solved problem back into an unsolved one. A chimney built for 130 degree gas kept its own flue above the acid dew point and stayed dry; a chimney fed by a wet scrubber discharges saturated gas at 50 degrees carrying sulphuric acid mist, so the inside surface runs wet with acid for the whole of a fifty-year design life. That is why the code classifies chimneys as dry, humid or wet by the humidity and temperature of the gas they carry, and why the choice of type and of anticorrosion scheme comes before any structural calculation. The document covers every part of the problem in turn: the basic requirements, including the fifty-year design working life and the rule that any chimney of 200 m or more, or serving a unit of 300 MW or more, is safety grade one; the selection of chimney type and the anticorrosion measures; the actions and their combinations, with separate treatment of wind load, earthquake action, thermal action, gas pressure, platform live load and dust load, ice load and construction load; then the three structural families - the single tube chimney, the single liner and multi-liner chimney, and the steel chimney, self-supporting or framed - each with its shell design and its construction measures, and for the liner types the brick, steel and fibre reinforced plastic options, the internal platforms and the flue frame. It continues with the subgrade and foundation design, the ancillary facilities that make a chimney operable and legal - lightning protection and earthing, aviation obstruction lighting and markings, internal lighting, the environmental monitoring platforms, the collection and discharge of flue gas condensate, the rain cover over the liner and the lift - and closes with the renovation of existing chimneys of each type. Two appendices give the calculation of cross-wind vibration of the shell, which is what governs a tall slender chimney, and the reinforcement calculation for openings in the shell. It was issued on 24 May 2024 by the National Energy Administration and took effect on 24 November 2024.

1.0.1 This standard is formulated in order to implement the construction policy of safety, reliability, economy and applicability in the construction of new chimneys and in the renovation of existing chimneys in fossil-fired power plants, and to control the engineering cost reasonably.

1.0.2 This standard applies to the design of newly built chimneys and to the renovation design of existing chimneys in fossil-fired power plants.

1.0.3 This standard does not apply to brick chimneys.

1.0.4 In addition to complying with this standard, the design of chimneys in fossil-fired power plants shall also comply with the provisions of the relevant current national standards.

2 Terms

2.0.1 chimney

A tall structure used to discharge the flue gas of a boiler.

2.0.2 dry chimney

A chimney discharging flue gas whose relative humidity is not higher than 60 percent and whose temperature is not lower than 90 degrees Celsius.

2.0.3 humid chimney

A chimney discharging flue gas whose relative humidity is higher than 60 percent and whose temperature is not lower than 60 degrees Celsius and not higher than 90 degrees Celsius.

2.0.4 wet chimney

A chimney discharging flue gas whose relative humidity is at saturation and whose temperature is not higher than 60 degrees Celsius.

2.0.5 shell

The load-bearing structure above the chimney foundation.

2.0.6 liner

The flue gas discharge tube inside the shell of a single liner or multi-liner chimney.

2.0.7 lining

A self-supporting structure supported in sections on the corbels of the shell, or a cast or masonry body attached directly to the shell by anchor bars distributed over it, which protects the insulation layer or the shell.

2.0.8 insulation

The structure placed between the shell and the lining so that the temperature to which the shell is heated does not exceed the specified maximum.

2.0.9 single tube chimney

A chimney in which the lining and the insulation layer are supported in sections directly on the corbels of the shell, or are bonded directly to the shell.

2.0.10 single liner chimney

A chimney in which one liner is placed inside the shell.

2.0.11 multi-liner chimney

A chimney in which two or more flue gas discharge tubes are placed inside the shell or inside the tower frame.

2.0.12 steel chimney

A chimney in which both the shell and the supporting structural system are of steel, including self-supporting steel chimneys and framed steel chimneys.

2.0.13 self-supporting steel chimney

A steel chimney whose stable structural system is formed mainly by the shell.

2.0.14 framed steel chimney

A steel chimney whose stable structural system is formed jointly by the supporting tower frame and the flue gas discharge tube.

2.0.15 flue frame

A steel or reinforced concrete structure used to support the horizontal flue.

2.0.16 fiber reinforced plastic liner

A liner made by a winding process, using synthetic resin as the matrix material and fibres and fibre products as the reinforcing material.

2.0.17 special-shaped chimney

A chimney whose shell has a non-circular cross-section.

2.0.18 flue gas condensate

The liquid formed when saturated flue gas condenses below the dew point temperature.

3 Basic requirements

3.1 General requirements

3.1.1 Apart from temporary structures, the design working life of a newly built fiber reinforced plastic liner should be 30 years, the design working life of newly built reinforced concrete chimneys, steel chimneys and single liner chimneys shall be 50 years, and the design working life for the renovation of an existing chimney shall be determined according to the remaining service life of that chimney.

3.1.2 The safety grade of a chimney shall not be lower than grade two; the safety grade of a chimney with a height of not less than 200 m, or serving a unit of not less than 300 MW, shall be grade one.

3.1.3 The durability design and the anticorrosion design of a chimney shall comply with the provisions of the current national standards GB/T 50010 Standard for design of concrete structures and GB/T 50046 Standard for anticorrosion design of industrial constructions.

3.1.4 The design of a chimney shall be carried out on the basis of the flue gas discharge conditions, the corrosivity grade of the flue gas, the structural reliability, the structural durability and the inspection and maintenance requirements of the unit, and after a comprehensive technical and economic comparison.

3.1.5 The design of the chimney structure and of its ancillary components shall use the limit state design method based on probability theory, shall measure the reliability of the structural members by the reliability index, and shall carry out the structural calculation using design expressions with partial factors. The design of the chimney subgrade and foundation may use the allowable stress method, the limit state method or the single safety factor method, and shall comply with the relevant provisions of the current national standards GB 50007 Code for design of building foundation and JGJ 94 Technical code for building pile foundations. The limit state design of the chimney structure and of its ancillary components shall include the ultimate limit state, in which the chimney structure or an ancillary component reaches its maximum bearing capacity, for example through strength failure, local or overall instability, or becoming unfit to continue bearing load because of excessive deformation; and the serviceability limit state, in which the chimney structure or an ancillary component reaches a limiting value of normal use.