Detection of cause of pipe burst in economizer of process CO steam boiler

O. STAMENKOVIĆ at al. DETECTION OF CAUSE OF PIPE BURST IN ECONOMIZER Detection of Cause of Pipe Burst in Economizer of Process co Steam Boiler OGNJEN S. STAMENKOVIĆ, University of Belgrade, Professional paper Faculty of Mechanical Engineering, Belgrade UDC: 658.1:665.6/.7(497.113) GORAN M. STUPAR, University of Belgrade, 621.184.2:539.4 Faculty of Mechanical Engineering, Belgrade DOI: 10.5937/tehnika2201055S DRAGAN R. TUCAKOVIĆ, University of Belgrade Faculty of Mechanical Engineering, Belgrade BOJAN M. BOŠKOVIĆ, Petroleum Industry of Serbia Head of Thermoenergetics Department Oil Refinery Pančevo, Pančevo In this paper results of analysis of process steam boiler operation with maximum continuous steam production of 75 t/h, steam pressure and temperature of 45,5 bar and 412 oC are presented. Steam boiler is predicted to operate within steam production facility of oil and gas refinery in Pančevo, Serbia. On the demand of purchaser steam boiler is enabled to operate with various fuels as well as with two or three fuels simultaneously. By fuels intake facilities it is enabled to introduce refinery gas, fuel oil and high-temperature waste gas to the boilers furnace. Waste gas is guided from FCC (Fuel catalyst cracking) facility and presents two-component fluid with polydisperse solid phase composed of particles of diameter smaller than 40 µm. Recent changes in steam consumption in refinery resulted in modifications in boiler`s operating regime and, further on, in significant changes in its operational parameters. At present, in new conditions, boiler operates with frequent pipe bursts on pipe bundles of boiler economizer which requires forced interruption in steam production as well as time and cost consuming operations for resuming boiler work. In this paper results of thermal calculations for design and new operational conditions are presented for the purpose of identification of cause of frequent unscheduled steam production interruptions. After analysis of presented results, recommendations on how to modify certain boiler operational parameters in order to eliminate or reduce possibility of such unfavourable occurance has been provided. Key Words: process steam boiler, waste gas, thermal calculation, economizer, pipe burst 1. INTRODUCTION Process steam boiler located in oil and gas refinery in Pančevo, Serbia, produces overheated steam utilized for domestic electricity production as well as for the needs of technological processes within refinery. Steam boiler operates since 1980. Recent changes in steam consumption in entire facility occurred which led to significant reduction of fresh steam flow rate in process steam boiler, even below minimum level. In such operational conditions pipe burst on economizer pipe bundles are frequent which requires immediate Author’s address: Ognjen Stamenković, University of Belgrade, Faculty of Mechanical Engineering, Belgrade, Kraljice Marije 16 e-mail: Paper received: 26.01.2022. Paper accepted: 07.02.2022. shutdown of steam boiler and unscheduled interruption in steam production. Such occurrence led to the reduction in boiler operational effectiveness, reliability and cost-effectiveness which requires conduction of analysis of boiler operational parameters in new working conditions in order to detect cause of such time and cost-consuming outages. In order to detect most influential parameters of boiler operation thermal calculation for boiler design parameters and new working conditions has been performed. By comparing the results of thermal calculations for various operational conditions cause of frequent pipe burst has been identified. Additionally, in order to verify fouling factors of all heat exchangers visual inspection of interior of flue gas tract has been conducted. 2. TECHNICAL OVERVIEW OF BOILER Process steam boiler is single-drum type with vertically aligned pipes in furnace, natural circulation TEHNIKA – MAŠINSTVO 72 (2022) 1 55 DETECTION OF CAUSE OF PIPE BURST IN ECONOMIZER 1.2. Overview of heat emitter and heat receiver streams 1.2.1. Heat emitter – flue gas stream In fig. 1 from [1] longitudinal section of process steam boiler with positions of all heat exchangers in flue gas tract is given. High temperature flue gas (heat emitter) generated in combustion process in furnace (1) exchange heat with wall pipes mounted on upper (2b), bottom (2c), front (2a), rear (2e) and back wall (2d) of furnace. Flue gas, at the end of furnace, turns and enters the horizontal convective flue gas channel formed of pipes on back and rear walls guided from furnace. First stage (3) and second (4) stage convective superheaters are located in horizontal flue gas duct. After superheaters convective heat exchanger (5) consisted of evaporator pipes extended from furnace back wall is positioned. At the end of horizontal duct flue gas turns downward and crosses through second pass vertical convective duct (7). In second pass convective duct convective evaporation bank tubes (6) are located. In this part of duct flue gas is guided by routing metal sheets for the purpose of intesifying heat transfer between heat emitter and heat receiver. At the end of second pass vertical duct convective heat exchanger (8) composed of convective evaporation bank tubes is located. Afterwards, heat emitter turns upward into third pass vertical convective duct (9). On the bottom of turning section two funnels (10) for separation of solid phase of combustion products are placed. In third pass convective duct flue gas crosses last heat exchanger in process boiler - two stages economozier (11). Outlet flue gas at the end of third pass convective duct turns into short horizontal duct (12) that guides flue gas to the long hoirzontal flue gas duct (14) via verticaly aligned interconnecting element (13). Through duct (14) flue gas is introduced into concrete-made stack and, further on, released to the atmosphere. 56 As air fan (15) is located upstream of the process steam boiler entire flue gas duct operates in pressurized draft regime (so called forced draft). Table 1. Design parameters of process steam boiler. Value Unit Parameter Notation in evaporator, three passes of heat emitter and force draught in flue gas tract. Boiler is able to operate with various fuels – refinery gas, fuel oil, and combination of waste gas with refinery gas or fuel oil. Due to the application of valid ecological norms operation of boiler with fuel oil has been avoiding for a while. Thus, in this paper operation of boiler with refinery gas only (RG regime) and simultaneous work with refinery and waste gas (RG+WG regime) has been considered. Design operational parameters for maximum continuous production when boiler utilizes two fuels - refinery and waste gas and refinery gas only are given in tab. 1. No O. STAMENKOVIĆ at al. RG+W G RG 1. Max. continous fresh steam mass flow rate D t/h 75 75 2. Outlet steam pressure ps bar 44,6 2 44,62 3. Outlet steam temp. ts (...truncated)