Carbon Detection Technology And Safety Assessment Of Organic Heat Transfer Heater

Abstract:According to special equipment accident circumstance bulletin made by AQSIQ (Administration of Quality Supervision, Inspection and Quarantine) in recent five years, the number of boiler accidents still stay high in the case of less boilers than before even though the rate of annual accident in per million devices was declined. From the further analysis of reason of accidents, we can learn that:In small and medium industrial boilers, fire accidents of organic heat transfer heater occurred frequently. To solve the problem of carbon deposition in organic heat transfer heater and fire accidents, this paper relies on two projects:special fund for quality supervision research in the public interest(201210080)-Organic heat transfer heater safety assessment and research on the key technology of carbon content on-line detection, and Quality inspection administration of science and technology plan project (2013QK212)-Organic heat transfer heater based on Modeling and Simulation of flow field of FLUENT, on basis of Systematic retrieval and in-depth analysis of previous research achievements, writer adopts research measure that combines theoretical analyses with practical application, and has a deep discussion which aims at carbon deposition in organic heat transfer heater, flow field distribution of medium FLUENT and safety assessment. The study includes following mainly innovative achievements:1. Based on the statistics and analysis of fire accidents of organic heat transfer heater in the past ten years in China and the relevant papers about detecting and controlling technology of carbon deposition in organic heat transfer heater, paper expounds main cause of fire accidents of organic heat transfer heater and points out that the key factor is carbon deposition in organic heat transfer heater.2. According to physicochemical property of the medium of organic heat transfer and the particularity of organic heat transfer heater, paper analyses formation mechanism of carbon deposition in organic heat transfer heater as well as operation mechanism of organic heat transfer heater, and proposes a detection method to measure the thickness of carbon deposition layer which based on ultrasonic guided waves.3. The writer designed and assembled a detecting system of carbon deposition in organic heat transfer heater. It tested cutoff frequency, transition frequency and group velocity of ultrasonic guided waves and the relationship between these three characterization parameters and variation of thickness of carbon deposition layer. Result indicates that:It is feasible to use group velocity of ultrasonic guided waves and monotonicity law of the variation in thickness of carbon deposition layer to detect thickness of carbon deposition layer, and feasibility of this detecting way can be further demonstrated by fitting test of frequency dispersion curve of group velocity through blank pipe.4. In order to identify the modal type of ultrasonic guided waves in detecting system of carbon deposition, paper used time-frequency analysis method to do the comparative analysis of multiple modals in tube, and combined with fitting of the main energy scatter gram by the time-frequency analysis and the trend of Modal L (0,2) in frequency dispersion curve of numerical simulation to deduce modal of main wave mode is Modal L (0,2). The relative error between group velocity and testing group velocity by time-difference method is only from1.88%to3.48%.5.According to the detecting test of the simulate attachment of the carbon deposition of ultrasonic guided wave, paper finds out that:the detecting blindness of group velocity of Modal L (0,2), which is drove by the situation that the signal is5period, the frequency rate is500kHz and the peak is200mV, is that the arrangement distance of probe should be less than350mm, and the best detecting arrangement distance of the detecting probe of the ultrasonic guided waves of carbon deposition layer in organic heat transfer heater's furnace tube is40cm. The SNR (Signal to Noise Ratio), time domain and the characteristics in frequency domain of the signal prove that the best period of detection is5periods; it can use epoxy resin to add hydrocarbon and to simulate carbon deposition layer, and it successfully drive the Modal L (0,2). When the distance of probe is 40cm and the detecting period takes5periods, paper use test to prove that group velocity of the Modal L (0,2) in carbon deposition pipe is less about7.65%than group velocity in the blank pipe, and this conclusion proves further that we could use changing relationship of group velocity in blank pipe and in carbon deposition pipe to detect carbon deposition layer in tube.6. The paper utilized the theory of ergonomics to the risk assessment of operation of organic heat transfer heater, and the paper got the conclusion that the weight of index of man-machine environment during the operation are:1.830,1.293and1.749, and by the comparison, paper finds out that the index of man and environment is0.5bigger than the weight of organic heat transfer heater itself. This result shows that the risk operation of organic heat transfer heater should put more attention to the people ware and environment management. Besides, from the statistics and the survey of fire accidents of organic heat transfer heater at home and abroad, the writer uses fishbone causal method analysis reason of accidents qualitatively, and finds out essential factor, the key factor (for example:the leak of organic heat transfer) with its importance and the key probabilistic by using the method of accident tree analysis and event tree analysis.7.The writer used FLUENT to do the simulate study of the coiled tube type of organic heat transfer heater with different flow velocities and different thickness of carbon deposition layer and finds out that:when there is no carbon deposition layer, the distribution of the flow velocity of organic heat transfer heater in the two side of tube wall is slower, particularly, the tube wall of radiant tube is more obvious; the flow velocity of organic heat transfer heater gradually increase from the tube wall to the center of the tube; in the radiant part, because the area of the turbulence level which has radiant heat is bigger than the level which has heat preservation, the flow velocity of the medium of organic heat transfer heater becomes the biggest when it comes close to the radiant tube wall and the junction of the laminar flow and the turbulence flow. When the inlet flow velocity comes to1.0m/s, with the lower flow velocity of conduction oil, organic heat transfer is in a degraded and deteriorated condition, and the local flow will have a disciplinary change with the change of pipe diameter and the flow velocity, the thinner of the carbon deposition layer, the better for the uniformity of flow field and the temperature of liquid membrane.The last but not the least, based on basement which built by the detection of carbon deposition in organic heat transfer heater, safety evaluation and the simulation of FLUENT flow velocity, the paper points out the management mode of the risk controlment of organic heat transfer heater and the advice of safety lawmaking.