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1、TECHNICAL SPECIFICATION CONTROL SYSTEM AND INSTRUMENTED PROTECTIVE FUNCTIONS FOR FIRED EQUIPMENT - System for an automatically-started, forced draught, multi-burner furnace or boiler (S 24.030 or S 24.034) DEP 32.24.20.38-Gen. July 1997 (DEP Circular 54/97 has been incorporated) DESIGN AND ENGINEERI
2、NG PRACTICE USED BY COMPANIES OF THE ROYAL DUTCH/SHELL GROUP This document is confidential. Neither the whole nor any part of this document may be disclosed to any third party without the prior written consent of Shell International Oil Products B.V. and Shell International Exploration and Productio
3、n B.V., The Hague, The Netherlands. The copyright of this document is vested in these companies. All rights reserved. Neither the whole nor any part of this document may be reproduced, stored in any retrieval system or transmitted in any form or by any means (electronic, mechanical, reprographic, re
4、cording or otherwise) without the prior written consent of the copyright owners. PREFACE DEP (Design and Engineering Practice) publications reflect the views, at the time of publication, of: Shell International Oil Products B.V. (SIOP) and Shell International Exploration and Production B.V. (SIEP) a
5、nd Shell International Chemicals B.V. (SIC) The Hague, The Netherlands, and other Service Companies. They are based on the experience acquired during their involvement with the design, construction, operation and maintenance of processing units and facilities, and they are supplemented with the expe
6、rience of Group Operating companies. Where appropriate they are based on, or reference is made to, national and international standards and codes of practice. The objective is to set the recommended standard for good design and engineering practice applied by Group companies operating an oil refiner
7、y, gas handling installation, chemical plant, oil and gas production facility, or any other such facility, and thereby to achieve maximum technical and economic benefit from standardization. The information set forth in these publications is provided to users for their consideration and decision to
8、implement. This is of particular importance where DEPs may not cover every requirement or diversity of condition at each locality. The system of DEPs is expected to be sufficiently flexible to allow individual operating companies to adapt the information set forth in DEPs to their own environment an
9、d requirements. When Contractors or Manufacturers/Suppliers use DEPs they shall be solely responsible for the quality of work and the attainment of the required design and engineering standards. In particular, for those requirements not specifically covered, the Principal will expect them to follow
10、those design and engineering practices which will achieve the same level of integrity as reflected in the DEPs. If in doubt, the Contractor or Manufacturer/Supplier shall, without detracting from his own responsibility, consult the Principal or its technical advisor. The right to use DEPs is granted
11、 by SIOP, SIEP or SIC, in most cases under Service Agreements primarily with companies of the Royal Dutch/Shell Group and other companies receiving technical advice and services from SIOP, SIEP or SIC. Consequently, three categories of users of DEPs can be distinguished: 1)Operating companies having
12、 a Service Agreement with SIOP, SIEP, SIC or other Service Company. The use of DEPs by these Operating companies is subject in all respects to the terms and conditions of the relevant Service Agreement. 2)Other parties who are authorized to use DEPs subject to appropriate contractual arrangements. 3
13、)Contractors/subcontractors and Manufacturers/Suppliers under a contract with users referred to under 1) or 2) which requires that tenders for projects, materials supplied or - generally - work performed on behalf of the said users comply with the relevant standards. Subject to any particular terms
14、and conditions as may be set forth in specific agreements with users, SIOP, SIEP and SIC disclaim any liability of whatsoever nature for any damage (including injury or death) suffered by any company or person whomsoever as a result of or in connection with the use, application or implementation of
15、any DEP, combination of DEPs or any part thereof. The benefit of this disclaimer shall inure in all respects to SIOP, SIEP, SIC and/or any company affiliated to these companies that may issue DEPs or require the use of DEPs. Without prejudice to any specific terms in respect of confidentiality under
16、 relevant contractual arrangements, DEPs shall not, without the prior written consent of SIOP and SIEP, be disclosed by users to any company or person whomsoever and the DEPs shall be used exclusively for the purpose for which they have been provided to the user. They shall be returned after use, in
17、cluding any copies which shall only be made by users with the express prior written consent of SIOP and SIEP. The copyright of DEPs vests in SIOP and SIEP. Users shall arrange for DEPs to be held in safe custody and SIOP or SIEP may at any time require information satisfactory to them in order to as
18、certain how users implement this requirement. All administrative queries should be directed to the DEP Administrator in SIOP. NOTE: In addition to DEP publications there are Standard Specifications and Draft DEPs for Development (DDDs). DDDs generally introduce new procedures or techniques that will
19、 probably need updating as further experience develops during their use. The above requirements for distribution and use of DEPs are also applicable to Standard Specifications and DDDs. Standard Specifications and DDDs will gradually be replaced by DEPs. DEP 32.24.20.38-Gen. July 1997 Page 2 TABLE O
20、F CONTENTS 1.INTRODUCTION.4 1.1SCOPE 4 1.2DISTRIBUTION, INTENDED USE AND REGULATORY CONSIDERATIONS4 1.3DEFINITIONS AND ABBREVIATIONS.4 1.4CROSS-REFERENCES5 2.GENERAL. 6 3.FUNCTIONAL (OPERATIONAL)DESCRIPTION7 3.1LOAD CONTROL7 3.2AIR/FUEL RATIO CONTROL7 3.3WASTE GAS FIRING8 3.4START-UP. 8 4.TECHNICAL
21、DESCRIPTION10 4.1IMPLEMENTATION CONSIDERATIONS.10 4.2LOCATIONS OF ALARMS, SWITCHES ETC11 4.3CALCULATION FORMULAE12 4.4DESCRIPTION OF INSTRUMENTED PROTECTIVE FUNCTIONS14 4.5IPF CLASSIFICATION AND CAUSE AND EFFECT DIAGRAM.21 5.REFERENCES23 APPENDICES APPENDIX 1Functional logic diagrams for a forced dr
22、aught multi-burner furnace 24 DEP 32.24.20.38-Gen. July 1997 Page 3 1.INTRODUCTION 1.1SCOPE This DEP specifies requirements and gives recommendations for control systems and instrumented protective functions for an automatically-started, dual-fuel fired, forced draught, multi-burner furnace/boiler w
23、ithout individual air shut-off dampers. This DEP may also be used for a furnace firing one fuel only, i.e. if the furnace is fired on gas only, all fuel oil related instrumentation may be disregarded, and vice versa. This DEP shall not be used for single burner systems or natural draught furnaces/bo
24、ilers. This DEP contains a control and IPF narrative and logic diagrams and refers to a standard specific process engineering flow scheme. Amended Per Circular 54/97 This DEP shall be used together with Standard Drawing S 24.030 (dual fuel) or S 24.034 (fuel gas). This DEP is written for systems whi
25、ch use DCSs for control and monitoring and PLC or Solid State / magnetic core type Instrumented Protective Functions. Accordingly, more use has been made of inverted signals than would have been the case for relay type IPFs. 1.2DISTRIBUTION, INTENDED USE AND REGULATORY CONSIDERATIONS Unless otherwis
26、e authorised by SIOP and SIEP, the distribution of this DEP is confined to companies forming part of or managed by the Royal Dutch/Shell Group, and to Contractors nominated by them (i.e. the distribution code is “C“, as defined in DEP 00.00.05.05-Gen.). This DEP is intended for use in oil refineries
27、, chemical plants, gas plants, onshore and offshore exploration and production facilities, and supply/marketing installations. If national and/or local regulations exist in which some of the requirements may be more stringent than in this DEP the Contractor shall determine by careful scrutiny which
28、of the requirements are the more stringent and which combination of requirements will be acceptable as regards safety, economic and legal aspects. In all cases the Contractor shall inform the Principal of any deviation from the requirements of this DEP which is considered to be necessary in order to
29、 comply with national and/or local regulations. The Principal may then negotiate with the Authorities concerned with the object of obtaining agreement to follow this DEP as closely as possible. 1.3DEFINITIONS AND ABBREVIATIONS 1.3.1General definitions The Contractor is the party which carries out al
30、l or part of the design, engineering, procurement, construction, commissioning or management of a project or operation of a facility. The Principal may undertake all or part of the duties of the Contractor. The Principal is the party which initiates, and ultimately pays for, the project. The Princip
31、al will generally specify the technical requirements. The Principal may also include an agent or consultant, authorised to act for the Principal. The word shall indicates a requirement. The word should indicates a recommendation. DEP 32.24.20.38-Gen. July 1997 Page 4 1.3.2Specific definitions Furnac
32、eIncludes both furnaces and boilers Instrumented protective functionA function comprising the Initiator function, Logic (IPF)Solver function and Final Element function for the purpose of preventing or mitigating Hazardous Situations. NOTE:The term “safeguarding“ is not widely used in this DEP becaus
33、e safeguarding relates not only to instrumented protective functions but also to protective equipment of a mechanical nature such as non-return valves, relief valves and bursting disks. 1.3.3Abbreviations ARWUAnti reset wind-up DCSDistributed control system IPFInstrumented protective function PEFSPr
34、ocess engineering flow scheme PLCProgrammable logic controller SRFStandard refinery fuel TSOVTight shut off valve 1.4CROSS-REFERENCES Where cross-references to other parts of this DEP are made, the referenced section number is shown in brackets. Other documents referenced by this DEP are listed in (
35、5). DEP 32.24.20.38-Gen. July 1997 Page 5 2.GENERAL This DEP shall be used as the basis for the control systems, IPFs, narratives, functional logic diagrams and PEFS for the installation for which it has been specified by the Principal. The Contractor shall prepare installation-specific narratives b
36、ased on this DEP, and shall add relevant tag numbers, set points, controller configurations, etc. The installation-specific narratives shall not contain general information which is not relevant to the specific installation. Like this DEP, the narrative shall contain a functional description includi
37、ng operational aspects and a detailed technical description. DEP 32.24.20.38-Gen. July 1997 Page 6 3.FUNCTIONAL (OPERATIONAL) DESCRIPTION 3.1LOAD CONTROL Flow control is the lowest level of control function for both gas and liquid fuel and for combustion air. Minimum combustion air flow is ensured b
38、y an adjustable mechanical minimum stop on the combustion air damper, while the maximum combustion air flow is limited by the capacity of the blower and air register resistance. Minimum fuel flows are ensured by minimum stop pressure controllers for both fuel oil and fuel gas, which guarantee a mini
39、mum burner load irrespective of the number of burners in operation. Similarly, maximum burner loads are limited by maximum stop pressure controllers. NOTE:The fuel pressure control limiters do not provide absolute limits to burner loads; with fuel gas, fuel gas density variations exert an influence;
40、 in (steam-atomised) fuel oil burners, fuel oil temperature and atomising steam pressure likewise exert an influence. In addition to the minimum stop fuel pressure controllers, the fuel control valves are provided with mechanical minimum stops. These are adjusted to correspond to minimum load with o
41、nly one burner in operation, and act as a pre-set valve position for start-up of the first burner. In multi-burner installations this may result in excessively low valve lifts when starting up the first burner(s), in which case the mechanical stop should be limited to at least 5% valve lift (which g
42、ives higher loads at the first burner start-up), or the use of parallel control valves (low and high capacity, acting in split-range) should be considered. Atomising steam for the fuel oil burners is controlled at a (constant) pressure differential relative to the burner fuel oil pressure. The furna
43、ce load controller (outlet temperature) acts on the fuel and combustion air flow controller set points via a “double-ratio cross-limiting“ system. The basic principle is that both fuel and combustion air flows are controlled in parallel, with limits (maximum for fuel, minimum for air) to avoid sub-s
44、toichiometric combustion. The control system works as follows: The output signal of the furnace outlet temperature (load) control can be adapted with signals from the furnace inlet temperature and/or the process coil flow in order to add a feed-forward control signal. The resultant signal, which rep
45、resents the total fuel demand, is then passed to the fuel flow controllers as follows: -the set point of the fuel gas flow controller is the total fuel demand, minus the (measured) fuel oil flow; -the set point of the fuel oil flow controller is the total fuel demand, minus the (measured) fuel gas f
46、low. NOTE:It is part of the design philosophy that only ONE fuel is on cascade load control at any time; the other fuel may be either out of operation or on local set point control, operator adjustable. Depending on the variation in the MW of the fuel gas, the fuel gas flow measurement shall be corr
47、ected for changes in gas density (see Section 4.3, Y3). This density compensation compensates for errors in flow measurement and for changes in stoichiometric air requirement. As the compensated signal also gives a reasonably accurate representation of heat input this signal is also used as input to
48、 the fuel flow controller. In this way the fuel gas flow controller indicates a flow in Standard Refinery Fuel (SRF). An additional indication of actual mass flow should be provided for mass balance purposes. 3.2AIR/FUEL RATIO CONTROL In parallel to adjusting the fuel flow, the total fuel demand sig
49、nal passes via the air/fuel ratio relay to adjust the set point of the combustion air flow controller. The required air/fuel ratio can either be manually set by the panel operator, or automatically set by a closed-loop stack oxygen controller. Limits should be set to the range over which the air/fue
50、l ratio can be adjusted, in order to prevent settings that correspond to sub-stoichiometric combustion. DEP 32.24.20.38-Gen. July 1997 Page 7 In addition to the basic parallel control system described above, limits are imposed on the adjustment of the set points of fuel and combustion air, as follow