GB/T 20475.2-2006Classification of the content of harmful elements in coal - Part 2: Chlorine (English PDF)

1 Scope

This part of GB/T 20475 specifies the ranges, names and codes into which coal is classified by dry-basis chlorine content, and the chlorine requirements for the production, processing and utilisation of coal.

It applies to coal exploration, production, processing, marketing and utilisation.

Small quantity, large damage

In a boiler chlorine volatilises as hydrogen chloride, and where the flue gas cools below the acid dew point - on the economiser, the air heater, the ductwork - it condenses and corrodes them.

In the superheater it takes part in the deposits that cause high-temperature corrosion of the tubes, one of the commonest causes of unplanned outages in coal-fired plant.

It also makes the ash stick

Chlorine lowers the melting point of the deposits, worsening fouling.

In a coke oven it passes into the gas and the by-product liquor and attacks the plant there, and it raises the corrosivity of everything leaving the site as residue or effluent.

And washing does not remove it

Much of the chlorine is associated with the inherent moisture and the organic matter rather than the mineral matter, so cleaning the coal barely touches it.

The only effective control is knowing the content in advance and blending or designing for it - which is exactly what a classification makes possible, by turning a laboratory number into a category that can appear in a resource statement, a purchase specification and a boiler design basis.

About this edition

GB/T 20475.2-2006 is the current edition. It was issued on 12 September 2006 and has been in force since 1 February 2007.

The interval between issue and effect is the transition period. It exists so that producers, laboratories and buyers can requalify products, revise procedures and use up documentation before the new text becomes the one that applies. The date on this page is the official one from the record of the Standardization Administration.

Classification and status

GB/T 20475.2-2006 is classified under ICS 73.040. ICS is the International Classification for Standards, the same scheme used by ISO and by the national bodies of most countries, which is what allows a Chinese standard to be placed beside its foreign counterparts on subject rather than on number.

Its Chinese Standard Classification code is CCS D 20. CCS is the domestic scheme, a letter for the sector and two digits for the subject within it, and it is the code by which the standard is filed and searched in China.

The GB/T prefix marks a recommended national standard. It is not, in itself, law: it becomes binding when a contract names it, when a regulation or a mandatory standard refers to it, or when a producer declares conformity with it. In practice that covers most of the cases in which it will be read — a purchase specification, an inspection agreement or a certification scheme.

How a Chinese national standard is set out

Chinese national standards are drafted to the rules of GB/T 1.1, which fixes the order in which a standard is set out. The document opens with a foreword recording the issuing bodies, the relationship to any previous edition and the technical committee responsible for it. Clause 1 is the scope. Clause 2 lists the normative references — the other standards that have to be applied together with this one, and without which its requirements cannot be met. Clause 3 gives the terms and definitions. The technical clauses follow: the requirements themselves, the test or measurement methods by which conformity is established, the inspection rules that say how a lot is sampled and judged, and, for a product standard, the provisions on marking, packaging, transport and storage. Annexes, normative or informative, come last.

GB/T 20475.2-2006 runs to 15 pages in the English translation. What is delivered is the complete document in that order: every clause, every table, every figure and every annex of the Chinese original, with the same numbering, so that a reference to a clause number in a contract or a test report points to the same place in both languages.

About this English translation

The English edition of GB/T 20475.2-2006 is a full translation of the official Chinese text, not a summary, an abstract or a machine rendering left unchecked. Clause and subclause numbers, table and figure numbers and annex letters are those of the original, because they are what a specification, a purchase order or a test report cites.

Technical terms are translated against the vocabulary standards of the same field, so that a term used in GB/T 20475.2-2006 reads the same way as in the other Chinese standards it is used beside. Where a term has an established English form in an ISO or IEC document on the same subject, that form is used; where China's term has no foreign counterpart, it is translated literally and the Chinese is kept alongside it rather than replaced by an approximation.

Quantities, units and symbols are carried over unchanged. Chinese standards use SI, so a value in the translation is the value in the original document, not a conversion, and a limit read from the English text is the limit that will be applied by a Chinese inspection body reading the Chinese one.

This page is compiled from the official publication record: the standard number and both titles, the issuing bodies, the dates of issue and effect, the ICS and CCS classification. The requirements, limits, tables and test conditions are in the document itself.