CALCIUM CARBIDE SPECIFICATIONS

Transcription

1 CALCIUM CARBIDE SPECIFICATIONS Doc 205/16 EUROPEAN INDUSTRIAL GASES ASSOCIATION AISBL AVENUE DES ARTS 3-5 B 1210 BRUSSELS Tel: Fax: info@eiga.eu Internet:

2 Doc 205/16 CALCIUM CARBIDE SPECIFICATIONS Prepared by WG-12 Acetylene Disclaimer All technical publications of EIGA or under EIGA's name, including Codes of Practice, Safety procedures and any other technical information contained in such publications were obtained from sources believed to be reliable and are based on technical information and experience currently available from members of EIGA and others at the date of their issuance. While EIGA recommends reference to or use of its publications by its members, such reference to or use of EIGA's publications by its members or third parties are purely voluntary and not binding. Therefore, EIGA or its members make no guarantee of the results and assume no liability or responsibility in connection with the reference to or use of information or suggestions contained in EIGA's publications. EIGA has no control whatsoever as regards, performance or non performance, misinterpretation, proper or improper use of any information or suggestions contained in EIGA's publications by any person or entity (including EIGA members) and EIGA expressly disclaims any liability in connection thereto. EIGA's publications are subject to periodic review and users are cautioned to obtain the latest edition. EIGA EIGA grants permission to reproduce this publication provided the Association is acknowledged as the source EUROPEAN INDUSTRIAL GASES ASSOCIATION AISBL Avenue des Arts 3-5 B 1210 Brussels Tel Fax info@eiga.eu Internet:

3 Table of Contents 1 Introduction Scope and purpose Scope Purpose Definitions Publications terminology Technical definitions Properties of calcium carbide Commercial sizes and dust content Porosity Impurities of calcium carbide Gas yield Purity of generated acetylene Sedimentation Briquettes Measurement of specifications Measurement of sedimentation Packing Marking References... 5 Table 1: Graded sizes of calcium carbide 2 Figure 1 Examples of sedimentation curves... 4 Figure 2 Example of sedimentation of lime... 5

4 1 Introduction This publication has been prepared by the European Industrial Gases Association (EIGA) to provide guidance on the relevant properties of calcium carbide to be used for the production of acetylene. This publication has collected information from calcium carbide manufacturers, withdrawn national standards and gas companies experience in order to establish an updated and current standard for calcium carbide to be used for the production of acetylene. 2 Scope and purpose 2.1 Scope Calcium carbide intended for the production of acetylene. 2.2 Purpose To provide guidance to EIGA Member Companies when they specify calcium carbide for acetylene production 3 Definitions 3.1 Publications terminology Shall Indicates that the procedure is mandatory. It is used wherever the criterion for conformance to specific recommendations allows no deviation Should Indicates that a procedure is recommended May and need not Indicate that the procedure is optional Will Is used only to indicate the future, not a degree of requirement Can Indicates a possibility or ability. 3.2 Technical definitions Briquette Compressed block of calcium carbide dust Calcium carbide When referred, shall meet the requirements of this publication. NOTE Calcium carbide is designated accordingly to its size, for example, calcium carbide of size 50 to 80mm is designated as calcium carbide 50/80. 1

5 3.2.3 Dust Calcium carbide that passes through a test sieve having a mesh width of 1 mm Gas yield Number of litres of crude acetylene obtained from a 1 kg sample prepared in accordance with 4.4. Gas yield is determined in l/kg and is corrected to 15 C and 1013 mbar moist, that is saturated at 15 C with water vapour Oversize of a given graded size calcium carbide Calcium carbide retained on coarser sieves Undersize of a given graded size calcium carbide Calcium carbide that passes through the finer sieves. Any needle like pieces remaining after the sieving operation are to be counted as part of the next finer size provided that they can be pushed through the holes by hand. 4 Properties of calcium carbide 4.1 Commercial sizes and dust content Calcium carbide is manufactured in the following graded sizes and designated accordingly: Size Particle size [mm] 2/4 2 to 4 4/7 4 to 7.1 7/ to 16 15/25 16 to 25 25/50 25 to 50 50/80 50 to 80 Table 1: Graded sizes of calcium carbide Other intermediate sizes are possible, for example 15/50, 15/80, 25/80. For some graded sizes there are specifications other than the simple particles size: Calcium carbide of a size 2/4 or above should not contain more than 5% by weight of oversize, and not more than 15% by weight of undersize, including dust. Furthermore, of this 15% by weight of undersize, at least 70% by weight should consist of the next finer size. The oversize should belong only to the next coarser size. Needle-like pieces should not, in a longitudinal direction, be more than 1 1/2 times the length of the corresponding upper limit of the particle size. Oversize pieces of calcium carbide size 50/80 must pass through a test sieve of 90mm hole size. Calcium carbide can exhibit the following dust content on delivery to the acetylene plant: For sizes 4/7 to 15/25 maximum of 2% by weight; and For sizes 25/50 and 50/80 maximum of 1% by weight. Some processes use small size calcium carbide with the addition of oil to reduce the blockages in calcium carbide feeders. 2

6 4.2 Porosity The porosity of the calcium carbide will impact the reaction in the generator. Increasing the porosity will increase the reaction speed and possibly introduce air into the generator. There is no specification for porosity, but this parameter should be taken into account when: Trying to find a reason for a fast, unexplained reaction speed in the generator; and Changing calcium carbide supplier. 4.3 Impurities of calcium carbide The following impurities can be found in calcium carbide: Inert substances; Free carbon: Should be less than 1% by weight; Ferrosilicon compounds: Should be less than 1,5% by weight; and Aluminium oxide- derived from the limestone used to produce the calcium carbide affects the sedimentation rate. 4.4 Gas yield To conform to this publication, calcium carbide shall show the following minimum average gas yields: Sizes 25/50 and 50/80: 300 l/kg Size 15/25: 280 l/kg Sizes 4/7 and 7/15: 260 l/kg The actual values obtained cannot be more than 3% below these figures; this is to take account of variations in sampling and in the analysis of the calcium carbide. No figures for the gas yield can be guaranteed for sizes under 4 mm. 4.5 Purity of generated acetylene The purity of the gas is generally measured in terms of its phosphine content. Where necessary, the hydrogen sulphide content is also determined. The content of phosphine is determined by colorimetric tubes. For many applications, the phosphine content of the crude acetylene is generally accepted as 0.06% by volume (600 ppm); some calcium carbide produces more than 600 ppm. Higher phosphine content can be reduced by using purifiers in the acetylene production process. When changing calcium carbide supplier, the phosphine content of the acetylene can change and require an updated chemical exposure risk assessment and possible impacts on user applications, for example flame quality and characteristics. 4.6 Sedimentation Calcium carbide produces lime slurry that will settle at different rates. In general, a fast settling slurry is good to separate water from slurry in a pond; a slow settling lime is good to avoid blockage of pipes in the low pressure parts of the plant. The selection of the calcium carbide is a plant specific activity and the measurement method is described below. Specific attention shall be paid to sedimentation when selecting calcium carbide, because the possible consequences could be the blockage of parts of the plant. 3

7 4.7 Briquettes The use of briquettes will impact the rate of reaction in comparison with a normal grade calcium carbide. One advantage of briquettes is the possibility to insert additives to modify the sedimentation rates. 5 Measurement of specifications For the measurement of the above properties refer to DIN 53922, Calcium carbide [1]. The standard is withdrawn, but the methods specified in it are still valid and compatible with current practices. 6 Measurement of sedimentation Sedimentation properties are not defined in DIN [1] and there is not a single sedimentation parameter to be used as a reference for defining the properties of generated lime. The main factors that influence sedimentation are: Ambient temperature; Content of aluminium (and also iron) content, measured as Al2O3: the lower the content, the faster the sedimentation rate; and Crystalline structure of calcium carbide formed during its production: this is influenced by the cooling speed. A method for determining settlement properties is to use settlement columns to conduct experiments where the % of lime over the initial volume is measured versus time Figure 1 Examples of sedimentation curves The sedimentation curve will then be compared with curve from a known and suitable calcium carbide, in order to verify if it satisfies the request. 4

8 7 Packing Figure 2 Example of sedimentation of lime The calcium carbide is to be supplied in containers conforming to the provisions of ADR, European Agreement concerning the International Carriage of Dangerous Goods by Road [2]. All containers in which calcium carbide is supplied shall be closed so that they are air and water tight and be filled as full as possible. For dispatch, the regulations appropriate to the means of transport employed shall be observed. According United Nations Manual of Test and Criteria [3] packing group I shall be assigned for this product. 8 Marking Calcium carbide conforming to this publication shall be marked on the container with the following details: Designation of the size grading; The manufacturer's name or symbol; ADR marks according Packing Group I; and Hazard label according to GHS. 9 References Unless otherwise specified, the latest edition shall apply. [1] DIN Calcium carbide (withdrawn) [2] ADR, European Agreement concerning the International Carriage of Dangerous Goods by Road, [3] United Nations Manual of Tests and Criteria 5