CODE OF PRACTICE FOR THE SAFE OPERATION OF THERMAL OIL HEATERS

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CODE OF PRACTICEFOR THE SAFE OPERATION OFTHERMAL OIL HEATERSIssued underSection 18A ofthe Boilers and PressureVessels OrdinanceOccupational Safety and Health BranchLabour Department

This publication is prepared by theOccupational Safety and Health BranchLabour DepartmentThis editionJuly 2017This publication is issued free of charge and can be obtained fromoffices of the Occupational Safety and Health Branch. Addressesand telephone numbers of the offices can be found in website of theDepartment at http://www.labour.gov.hk/eng/tele/content.htm.This publication may be freely reproduced except for advertising,endorsement or commercial purposes. Please acknowledge the sourceas “Code of Practice for the Safe Operation of Thermal Oil Heaters”,published by the Labour Department.

CODE OF PRACTICEFOR THE SAFE OPERATION OFTHERMAL OIL HEATERSIssued under Section 18A ofthe Boilers and Pressure Vessels Ordinance

CONTENTSINTRODUCTIONLIST OF APPLICABLE ORDINANCE AND REGULATIONSPagesiiiiCHAPTER 11.GENERAL11.1 Purpose and Scope11.2 Interpretation1CHAPTER 22.ESSENTIALS OF THERMAL OIL HEATER32.1 General32.2 Description of the Thermal Oil System32.3 Requirements of a Heat Carrier42.4 Essential Fittings52.4.1 Safety Valve52.4.2 High Thermal Oil Temperature Cutout Alarm62.4.3 Thermal Oil Flow Limiter62.4.4 Low Oil Level Cutout in Expansion Tank72.4.5 Thermal Oil Heater Control7

CHAPTER 33.OPERATION AND MAINTENANCE83.1 Start Up83.1.1 Preparation for Start Up83.1.2 Inspection93.1.3 Start Up from Cold93.2 Observation during Operation113.3 Operation Data113.4 General Precautions when Operating a Thermal Oil Heater123.5 Precautions to be observed on shutting down a13Thermal Oil Heater3.6 Routine Maintenance133.7 Common Faults in Operating Thermal Oil Heater153.7.1 Overpressure153.7.2 Low Thermal Oil Flow Rate163.7.3 High Thermal Oil Temperature163.7.4 Low Oil Level in Expansion Tank163.7.5 Abnormal Differential Thermal Oil Temperature173.7.6 Abnormal Noise and Vibration173.7.7 Further Points to be Noted17

CHAPTER 44.SAFETY REQUIRMENTS IN OPERATION AND MAINTENANCE19CHAPTER 55.FIRE PRECAUTIONS, FIRE FIGHTING AND EQUIPMENT215.1 Fire Hazard215.2 Precautions225.3 Fire Fighting235.4 Fire Fighting Equipment245.4.1 Foam Fire Extinguisher245.4.2 Dry Powder Fire Extinguisher255.4.3 Carbon Dioxide Fire Extinguisher265.5 Fire Drill26CHAPTER 66.ACCIDENTS AND DEFECTS27CHAPTER 77.BASIC KNOWLEDGE OF ELECTRICITY297.1 Basic Knowledge297.2 Basic Terms of Electricity297.3 Safety Precaution30

CHAPTER 88.FIRED THERMAL OIL HEATER318.1 Essential Fittings318.1.1 Flue Gas Temperature Limiter318.1.2 Flame Detector318.2 Common Faults in Operating Fired Thermal Oil Heater328.2.1 Fuel Burner Misfire328.2.2 High Flue Gas Temperature328.3Uptake Fire338.4Basic Knowledge of Combustion34

INTRODUCTIONThe Boilers and Pressure Vessels Ordinance, Chapter 56, sets out the provisionsrelating to the control in the use and operation of boilers and pressure vesselsin Hong Kong. Boiler includes a vessel in which oil is heated at a pressuregreater than atmospheric pressure and therefore covers thermal oil heaters.This Code of Practice is issued by the Boilers and Pressure Vessels Authorityunder section 18A of the Ordinance for the purpose of providing guidance inorder to ensure safe operation of thermal oil heaters.Under section 18A(2) of the Ordinance, any person who fails to observe theprovisions of this Code shall not render himself liable to criminal proceedingsof any kind, but any such failure may, in any proceedings whether civil orcriminal and including proceedings for an offence under the Boilers andPressure Vessels Ordinance, be relied upon by any party to the proceedingsas tending to establish or to negative any liability which is in question in thoseproceedings.These thermal oil heaters must be operated safely and dependably andremain serviceable for years, with cleaning and maintenance for the mostpart being undertaken during pre-planned maintenance periods. The safetyand dependability built into thermal oil heaters is by rigorous compliance ofall manufacturer’s instructions, relevant codes and standards for regulatingdesign, fabrication and inspection of the thermal oil heaters and their auxiliaryequipment.For the requirement on fire services, installations and equipment, please seekadvice from the Fire Services Department.i Code of Practice for the Safe Operation of Thermal Oil Heaters

For the requirement on the installation and maintenance of electrical supply tothe thermal oil heater including electrical parts, please seek advice from theElectrical and Mechanical Services Department.The Commissioner for Labour has been appointed as the Boilers and PressureVessels Authority.The Authority has authorized the Principal Surveyor toperform and exercise some of the functions, duties or powers under theOrdinance.EnquiryIf you wish to enquire about this Code of Practice or require advice on theregulation of boilers and pressure vessels, please contact the Boilers andPressure Vessels Division of the Labour Department through:TelephoneFaxE-mail:::3107 34582517 6853enquiry@labour.gov.hkInformation on the services offered by the Labour Department and on majorlabour legislation is also available on our website at http://www.labour.gov.hk.For details on the services offered by the Occupational Safety and HealthCouncil, please call 2739 9000.ComplaintsIf you have any complaint about unsafe workplaces and work practice, pleasecall the Labour Department’s occupational safety and health complaint hotlineat 2542 2172. All complaints will be treated in the strictest confidence.Code of Practice for the Safe Operation of Thermal Oil Heatersii

LIST OF APPLICABLE ORDINANCE ANDREGULATIONS(a)Boilers and Pressure Vessels Ordinance, Cap. 56(b)Boilers and Pressure Vessels Regulations(c)Boilers and Pressure Vessels (Forms) Order(d)Boilers and Pressure Vessels (Exemption) (Consolidation) Orderiii Code of Practice for the Safe Operation of Thermal Oil Heaters

CHAPTER 11.GENERAL1.1 Purpose and ScopeThe purpose of this Code of Practice is to promote the safe operationof thermal oil heaters.This Code may also offer practical guidance for those responsiblefor the safety and direct supervision of thermal oil heaters.The scope of the Code is limited to such basic information as isnecessary for the safe operation of thermal oil heaters.1.2 InterpretationFor the purpose of this Code:“Authority” means Boilers and Pressure Vessels Authority;“boilers” means any closed vessel in which for any purpose steamis generated under pressure greater than atmospheric pressureand also means any economizer used to heat water being fed intoany such vessel, any superheater used for heating steam and anyfitting directly attached to such vessel that is wholly or partly underpressure when steam is shut off, and any vessel in which oil is heatedat a pressure greater than atmospheric pressure;“boiler inspector” means a person who has been appointed by theAuthority to be a boiler inspector and whose appointment to be aboiler inspector has not been suspended;Code of Practice for the Safe Operation of Thermal Oil Heaters1

“certificate of competency” means a certificate of competencyissued by the Authority;“certificate of fitness” means a certificate of fitness issued undersection 33 of the Boilers and Pressure Vessels Ordinance;“competent person” means a person whose name is for the timebeing entered in the register of competent persons kept pursuant tosection 7(1)(e) of the Boilers and Pressures Vessels Ordinance;“Ordinance” means Boilers and Pressure Vessels Ordinance (BPVO);“owner”, in relation to a boiler or pressure vessel, includes anyperson who is in possession of the boiler or pressure vessel underan agreement of hire purchase or under a contract between asupplier of boilers or pressure vessels, or the agent of any suchsupplier, and such person for the sale of the boiler or pressurevessel, notwithstanding that the property in the boiler or pressurevessel has not passed to such person, and, where the owner of aboiler or pressure vessel cannot be found or ascertained or is absentfrom Hong Kong or is under disability, also includes the agent of theowner;“pressure vessel” means a steam receiver, an air receiver and aportable gas generator;“recognized inspection body” means an independent inspectionbody recognized by the Boilers and Pressure Vessels Authority.2 Code of Practice for the Safe Operation of Thermal Oil Heaters

CHAPTER 22.ESSENTIALS OF THERMAL OIL HEATER2.1 GeneralThermal oil heater is normally operated below the boiling point ofthermal oil. The operating pressure is the pump pressure to circulatethe thermal oil through the heater with sufficient flow to preventoverheating of thermal oil.Thermal oil is a flammable substance which can produce flammablemist to induce fire and explosion hazards at high temperature.Control of the working temperature of thermal oil is important for thesafe operation of thermal oil heaters.The furnace for the fired thermal oil heater is the high risk space inwhich an explosive gas may accumulate when thermal oil or fuel oilis leaked into the furnace.Thermal oil heaters have been involved in serious accidents abroad.This equipment should be operated with great care. The personnelengaged in operation and maintenance of these heaters shouldbe fully conversant with correct operating procedures and safetydevices as given in the manufacturer’s manual. The essential devicesfor operation and safety of this equipment are given below.2.2 Description of the Thermal Oil SystemThermal oil system is a heat carrier (thermal oil) heating plantcomprised of thermal oil heater, circulating pump, heat consumingdevice, expansion tank, storage tank, de-aerator, piping and controlpanel.Code of Practice for the Safe Operation of Thermal Oil Heaters3

Thermal oil heater is usually of the tube coil type, which can bevertical or horizontal. It can be heated electrically or fired by fuel toraise temperature of the thermal oil.Thermal oil which circulates through the system is firstly raised toa temperature of about 300 degree C in the thermal oil heater. Theheated oil then flows to the heat consuming devices to transfer heatenergy for heating purposes. A temperature drop of approximately40 degree C in the consuming devices is usually anticipated. Afterthe heat has been absorbed, the thermal oil is returned to the thermaloil heater by means of a circulating pump.An expansion tank is provided in the system to take up expansion ofthe thermal oil when it is heated. A de-aerator is sometimes installedfor removing air in the system. A storage tank, having a capacitysufficient to contain all the oil in the system, is also installed. In caseof any emergency or repairs, the entire contents in the system canbe emptied into this storage tank.2.3 Requirements of a Heat CarrierThe main requirements for an ideal heat carrier are:(a)(b)(c)(d)(e)(f)(g)high boiling point;low solidification temperature;good thermal stability;low viscosity;good heat transfer properties;low corrosion tendency; andnon-toxic and odourless.4 Code of Practice for the Safe Operation of Thermal Oil Heaters

Commonly used thermal oils have the following significantadvantages over water:(a)(b)(c)(d)higher boiling point at atmospheric pressure;low tendency for corrosion or formation of scale;no need to carry out regular treatment; andno expansion during solidification.The properties of a typical thermal oil are:Density at 200 C760 kg/m3Specific Thermal Capacity2.4 kJ/kgKFlash Point180 CIgnition Point370 CBoiling Point330 CPour Point-18 CCoefficient of Thermal Expansion0.00076 / C2.4 Essential Fittings2.4.1. Safety ValveIts function is to prevent the thermal oil heater from operatingat a pressure exceeding the maximum permissible workingpressure. It should be connected directly to an independent oiloutlet of the thermal oil heater and no valve should be placedin between. The safety valve should be vertically placed.When an easing gear is fitted in order to lift the valve from itsseat, it should be actuated once a day and the valve shouldbe tested by oil pressure every week.Code of Practice for the Safe Operation of Thermal Oil Heaters5

The discharge piping of a safety valve should be connectedto the top of a closed vented expansion tank or storage tank.If a safety valve is installed on the circulation pump, then itsdischarge should connect to the suction of the pump.2.4.2 High Thermal Oil Temperature Cutout AlarmIt is a temperature cutout switch which is used to safeguardthe physical properties of the thermal oil and prevent thethermal oil heater from overheating. Overheating will lead torapid deterioration of the thermal oil. If the temperature ofthe thermal oil has reached the setting value of the controlthermostat, the fuel burner or electric heating element will beshut down automatically.One method of testing the temperature cutout switch is to setthe working temperature higher than the cutout temperatureby changing the setting value of the control thermostat. Thethermostat set value must be brought back to the normalvalue after the testing.2.4.3 Thermal Oil Flow LimiterIt is in a form of differential pressure switch installed acrossthe oil inlet and outlet of the thermal oil heater. If the flow ofthe oil is interrupted by any blockage found inside the oil pipeor by failure of the circulating pump, the fuel burner or electricheating element will be cut out.6 Code of Practice for the Safe Operation of Thermal Oil Heaters

2.4.4 Low Oil Level Cutout in Expansion TankAny loss of thermal oil due to leakage can be indicated by thisdevice which will shut off the fuel burner or electric heatingelement. The leakage is usually found on heater tubes, shaftseals of circulating pump, pipeline and flanges of the system.If the leakage from the fuel burner happens inside the furnace,explosion may occur.2.4.5 Thermal Oil Heater ControlThe main parameter controlling thermal oil heater is theworking temperature. The role of the operating pressure, isnot so prominent because any change of pressure will notaffect the working temperature of the system. Furthermorethe pressure in the system is basically the discharge pressureof the circulating pump only.When the temperature of the oil inside the thermal oil heaterhas attained the upper temperature setting limit, the heatinput will be stopped but the circulating pump would runcontinuously. When the temperature of the oil has attainedthe lower temperature setting limit, the fuel burner or electricheating element will again be actuated by the thermostat.Code of Practice for the Safe Operation of Thermal Oil Heaters7

CHAPTER 33.OPERATION AND MAINTENANCEThe safety and reliability of thermal oil heaters require proper attention notonly while they are being designed, manufactured and erected, but also,while they are in service.Modern thermal oil heaters are capable of operating for long periodsof service. Successful operation requires adherence to basic operatingprinciples, and it requires the thermal oil heater to be maintained inproper operating condition by performing the necessary in-service andpreventive maintenance.Operation and maintenance manuals and instructions provided by thethermal oil heater manufacturer should be understood and strictly followedby all personnel involved.Proper and adequate training including the electrical safety should beprovided for the Competent Person, in particular for those medium tolarge size thermal oil heaters.All record books or oil reports required by this Code should be kept bya responsible person for as long as practicable for reference, otherwisebe kept for a continuous period of the recent 3 years or since registrationand put to use.3.1 Start Up3.1.1Preparation for Start UpAll preliminary operations for testing and cleaning of thethermal oil heater should be performed by experiencedCompetent Persons. They should have the knowledge andexperience to ensure the safe operation of thermal oil heaterby correct adjustment of controls, interlocks and cutouts.8 Code of Practice for the Safe Operation of Thermal Oil Heaters

Every new thermal oil heater or any thermal oil heater thathas undergone major repairs or alterations must be preparedfor putting back into service through various steps, such asinspection, hydrostatic testing and safety valve setting andtesting.3.1.2 InspectionAn inspection of thermal oil heater and its auxiliary equipmenthas two purposes. It verifies the conditions of the thermaloil heater so that appropriate remedial action can be doneif required. It familiarizes the Competent Person with theequipment so that proper control on the operation of thethermal oil heater can be achieved.3.1.3 Start Up from ColdThe following procedures are to be followed when starting athermal oil heater from cold condition:(a)Read and be fully conversant with the detailedoperating instruction for the thermal oil heater and itsauxiliaries;(b)Check the Certificate of Fitness for the thermal oilheater to ensure that it does not expire; be awarethat the approved maximum permissible workingpressure is indicated on the pressure gauge by a redline; and know the maximum permissible workingtemperature;(c)Check the thermal oil heater and its associatedequipment to ensure that they are in normal workingcondition;Code of Practice for the Safe Operation of Thermal Oil Heaters9

(d)For fired thermal oil heater, check if the fuel systemincluding fuel tank, pipeline and valves are in order,and clean all fuel filters;(e)Clean all the thermal oil filters;(f)Check if the thermal oil level at the expansion tank isnormal and all the pipelines are securely connectedwith no visual loose connection or leakage;(g)Check if the boiler room is clean and well ventilated;(h)Check for the availability and condition of fireextinguishing equipment;(i)Visually check that the electricity supply is securelyconnected and there are no visual loose connectionsor exposed electric wires;(j)Switch on the main supply and ensure that the sourcelight is lit;(k)Start the circulating pump to get the thermal oil flowingthrough the thermal oil system;(l)For electric thermal oil heater, switch on the electricheating element.(m)For fired thermal oil heater, before the fuel dischargedfrom the burner is ignited, the furnace must bethoroughly purged in order to expel any explosivemixture accumulated inside the furnace. The purgingprocess must be repeated for each time the firingsequence is commenced;10 Code of Practice for the Safe Operation of Thermal Oil Heaters

(n)Adjust the set temperature from low to the desiredvalue incrementally according to the manufacturer’srecommendation.3.2 Observation during OperationThe following observations should be made and monitored constantlywhen operating a thermal oil heater:(a)pressure, temperature and flow rate of the thermal oil;(b)thermal oil level in the expansion tank;(c)combustion condition inside the furnace (for fired thermaloil heater), and the proper operation of the electric heatingelement (for electric thermal oil heater);(d)noise and water hammer found in the pipeline due to thepresence of water in the thermal oil system;(e)the temperature difference between outlet and inlet of thethermal oil heater;(f)any leakage found at pipelines, level gauge, flanges and shaftseals of the circulating pump; and(g)the running condition of the circulating pump.3.3 Operation DataThe following readings should be recorded at regular intervals:(a)inlet and outlet oil temperature of thermal oil heater;(b)thermal oil pressure of the circulating pump and the thermaloil heater;(c)thermal oil flow rate;(d)thermal oil level in expansion tank;Code of Practice for the Safe Operation of Thermal Oil Heaters11

(e)thermal oil differential pressure between inlet and outlet ofstrainer;(f)flue gas temperat

energy for heating purposes. A temperature drop of approximately 40 degree C in the consuming devices is usually anticipated. After the heat has been absorbed, the thermal oil is returned to the thermal oil heater by means of a circulating pump. An expansion tank is provided in the system to take up expansion of the thermal oil when it is heated.

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