卧式杀菌锅加压水杀菌的热分布问题

概述参照美国FDA和NCA的有关规定,对杀菌锅的热分布要求大致如下:(1)GMP要求杀菌锅内各点都达到预定的杀菌温度才开始杀菌计时。(2)热分布需测定24个点,最少不能少于12个点的温度。考虑到目前我国使用的卧式杀菌锅长度较短(3米左右)以及测试手段的限制,一般测定12个点的温度已够。(3)考虑到操作对热分布的影响较大,因此,最好采用多点温度记录仪一次完成12个点温度的测定。分多次测定则包含了操作差异的影响,给热分布是否均匀的判断带来困难。     

卧式旋转蒸汽杀菌锅热分布的改进研究

杀菌锅的热分布均匀性是罐头类食品杀菌良好操作规范的重要指标,也是确保罐头类食品安全性的关键。目前,国家也有针对性地制定了食品热力杀菌设备热分布测试规程,该规程虽尚未正式发布,但明确了食品热力杀菌设备的热分布要求,本文结合该要求,对生产使用的卧式旋转杀菌锅热分布情况进行了跟踪及改进,以确保能够达到标准规定的要求。     

杀菌锅的热分布测试

<正> 目前我国用于罐头食品杀菌的装置主要是静止式杀菌锅。静止式杀菌锅分为立式和卧式两种。静止式杀菌锅的热分布是指排气结束时锅内规定各点的混度值及相对状况。排气结束时,如果锅内各点的温度之差小于1°F(约相当于0.5℃)则为热分布均匀,如果大于1°F,则为热分布不均匀。例如某一产品的杀菌公式为10′—35′/116℃,如果所用的杀菌锅热分布不均匀,在升温结束后,锅内就可能有某些区域或点的温度达不到116℃。这样经35分钟杀菌     

回转杀菌机的研究(续)

本文从传热学原理分析了设计回转杀菌机的依据。本机系全自动控制、用过热水作为加热介质、杀菌时处于回转状态。与静置式杀菌机比较,本机具有缩短了杀菌时间、提高了罐头产品质量、节约了蒸汽和冷却水等优点。全机由杀菌锅和贮水锅组成,贮水锅置于杀菌锅的上方。填满罐头的杀菌篮放于杀菌锅内:贮水锅用于制备过热水。本机的突出优点是杀菌锅的热分布均匀。自动操作程序可分为八个工序:1.制备过热水;2.把贮水锅中的过热水注入杀菌锅;3.杀菌锅升温;4.杀菌;5.热水回收;6.冷却;7.排水;8.启锅。本文还详细地讨论了本机的工艺试验结果。     

回转杀菌机的研究

本文从传热学原理分析了设计回转杀菌机的依据。本机系全自动控制、用过热水作为加热介质、杀菌时处于回转状态。与静置式杀菌机比较、本机具有缩短杀菌时间,提高罐头产品质量、节约蒸汽和冷却水等优点。全机由杀菌锅和贮水锅组成,贮水锅置于杀菌锅的上方。填满罐头的杀菌篮放于杀菌锅内:贮水锅用于制备过热水。本机的突出优点是杀菌锅的热分布均匀,自动操作程序可分为八个工序:1.制备过热水;2.把贮水锅中的过热水注入杀菌锅;3.杀菌锅升温;4.杀菌;5.热水回收;6.冷却7.排水8.启锅。本文还详细地讨论了本机的工艺试验结果。     

基于PLC的杀菌锅控制系统设计

根据罐类产品杀菌工艺要求,针对原有杀菌锅存在的一些问题,设计了一套基于PLC的杀菌锅自动控制系统,详细介绍了系统的结构和工作原理、硬件配置、软件设计和调试经验。系统经八宝粥厂实际运行检验证明,该系统提高了杀菌锅运行的可靠性和自动化水平、提升了杀菌质量,降低了能耗,能同时适应多种罐类产品杀菌工艺要求,同时通过对杀菌锅的泄汽管路和控制方式的改进,有效降低车间温度、湿度、噪音,在实现热能回收的同时,降低了车间蒸汽消耗。     

冷藏罐装蟹肉杀菌工艺特点的研究

本论文研究了出口冷藏罐装蟹肉巴氏杀菌工艺特性.通过测定杀菌锅与冷却池的热分布及杀菌时罐内冷点处温度值的变化,获得相关的传热曲线.通过分析热穿透数据计算出其F0值的大小,探讨了该杀菌工艺与设备的适用性.研究结果表明该工艺使产品杀菌过度,设备传热效果不佳,极易造成锈罐,急需进行改良.     

蒸煮杀菌锅控制温度的自动化

<正> 在罐头食品生产过程中,蒸煮杀菌工艺为一道重要工序,因此准确掌握杀菌锅温度及升温、杀菌时间是保证罐头产品质量的一个重要环节。目前国内大多数罐头食品厂的杀菌工序均以人工手操阀门来进行生产,不但产品质量不够稳定,操作工人在高温锅旁操作时亦须付出繁重的劳力。如何使杀菌锅配上新颖仪表使控温自动化,成为当前罐头食品行业提出的一个新课题。     

理想的高温杀菌设备LH4A20高压淋水式杀菌锅

惠州市乐惠实业有限公司在引进消化吸收国外技术的基础上，自行设计制造了LH4A20淋水式杀菌锅。该杀菌锅属于高温静止式间歇杀菌设备，主要应用于饮料、罐头或方便面食品和医药针剂等的高温高压杀菌，尤其适用于软罐头和玻璃瓶罐头的杀菌。ILH4A20淋水式杀菌锅主要性能特点1．1采用了大流量循环水加热，杀菌锅底部贮水约400L。当杀菌时，循环泵把水箱中的杀菌水经过滤器送到加热器中进行加热，然后从顶部的淋水板均匀淋在所需杀菌的产品上面，循环泵以每小时400次的速度将锅内的杀菌水循环。锅内温度非常均匀，热量传递理想。1．2冷却水…     

带有循环风机的杀菌锅——保持杀菌温度的均一性

罐头食品的杀菌温度直接关系到产品质量。在进行杀菌操作时如何保持杀菌锅内各部分温度的均匀一致,往往是生产工艺制订者和操作者十分关心的问题;也是杀菌设备设计工作者必须重视的课题。当然,最终的目的是要保证在同一锅内进行杀菌的所有罐头都能获得杀菌工艺所制订的F值,不致有偏高或不足的情况发生。     

Heat Distribution in Industrial-scale Water Cascading (Rotary) Retort

A heat distribution study was performed in an industrial-scale 4-basket water cascading rotary retort under fully loaded operating conditions. Detailed analysis of the temperature distribution basket-by-basket was followed by an evaluation of the temperature distribution throughout the retort (at 0, 4 and 7 rpm). Finally, a heating rate distribution study, using silicone elastomer food-simulants, was carried out to evaluate heat transfer uniformity throughout the retort. Results revealed that for static processes the slowest heating zone was located at the bottom of the basket at the back of the retort, whereas for rotary processes the center of this basket was heated slowest. Heating rate distribution results indicated uniform heat transfer throughout the retort.     

Nonuniformity in Lethality and Quality in Thermal Process Optimization: A Case Study on Color Degradation of Green Peas

ABSTRACT: In a case study on green peas, nonuniformity in microbial lethality and nonuniformity in quality retention (color) in retort processing was investigated by combining nonuniformity in the product (heat penetration data) and nonuniformity in the retort (heat distribution data) through simulations. The fractional conversion model was applied to model the color degradation of peas. The temperature dependence of color degradation decimal reduction times could be described by TDT (Thermal Death Time) equations with a z-value of 47.5 ± 5.9 °C. Heat penetration trials were conducted on peas in brine to determine the variability in heating parameters. A theoretical optimization procedure was carried out, and an experimental verification of the calculated results was conducted.     

Comparison of Sterilization Values from Heat Penetration and Spore Count Reduction in Agltating Retorts

Sterilization values from heat penetration (F_o) and spore count reduction (IS) were simultaneously measured in 7% food starch heated in 300 × 404 cans in an agitating retort. Thermal inactivation of the spores of Bacillus stearothermophilus was characterized by a 4 min lag period, a D_121.1 of 2.5 min, and a z of 8.2C°. Differences between IS and F_o were influenced by retort temperature, lag in inactivation, and z-value, for F_o values from 5 to 15. IS was generally higher than F_o for retort temperatures above 121.1°C. F values using the z of 8.2°C compared favorably to IS (corrected for the inactivation lag period) for retort temperatures between 115.0° and 126.1°C.     

Comparison of heat transfer rates during thermal processing under end-over-end and axial modes of rotation

Thermal processing under conditions enabling container agitation are attractive to food processors since they provide higher rates of heat transfer and more uniform temperature due to product mixing. Two common types of agitations are end-over-end and axial agitation. While end-over-end agitation is common in batch retorts, axial agitation is predominant in continuous cookers in which the cans roll in a helical path along the retort shell. In this study, heat transfer rates to canned Newtonian fluids in end-over-end and axial modes of rotation were evaluated in the same retort. A single basket rotary retort was retrofitted to accommodate simultaneously both end-over-end and two types of axial modes of rotation, free axial and fixed axial. In the free axial rotation, the cans were allowed to rotate on their own axis as they rolled along the retort shell during the bottom third of the rotation, while in the fixed axial mode, the cans in the axial direction were held stationary in the rotating basket. The overall heat transfer coefficient U, heating rate index, lag factor and cook values associated with cans filled with Newtonian fluids were evaluated using a central composite rotatable design of experiments with glycerin at five concentration level (no glycerin to all glycerin), heating medium temperature (111.6-128.4 °C) and five basket-rotational speeds (4-20 rpm). Higher U, and lower heating rate index, lag factor and cook values were associated with higher rotational speed and retort temperatures for all modes of agitation. The heat transfer parameters associated with free axial rotation were significantly higher than in the end-over-end mode which was higher than in the fixed axial mode.     

Establishing Thermal Processes for Products with Broken-Heating Curves from Data Taken at Other Retort and Initial Temperatures

Heat penetration data were obtained at high and low retort temperatures and at high and low product initial temperatures in two can sizes for five products displaying broken heating in a still retort. Extrapolation of data to a higher retort temperature was found to be an acceptable (conservative) practice for process establishment. For 300 × 400 cans of corn in brine predicted processing time was 9.7 min for a 128°C process on the basis of data obtained at 116°C. The actual required time was 8.5 min. Conversely, data extrapolated to a lower retort temperature were not acceptable. Initial temperature influenced processing times by as much as 50% for some products; the highest initial temperature intended for establishment of the process must be used for the heat penetration test.     

Determining convective heat transfer coefficient during sterilisation of canned evaporated whole milk

The effect of retort temperature, rotation speed, headspace and radius of rotation on mean convective heat transfer coefficient during sterilisation of canned evaporated whole milk was studied. The mean total solids content of evaporated milk obtained in a pilot plant installation was 25.25 g/100 g. Processing variables used ranged as follows: retort temperature: 117-123 °C; speed of rotation: 10-20 rpm; headspace: 4-12 mm; radius of rotation: 3.5-16.5 cm. The model developed for heat transfer coefficient was adequate, showing no significant lack of fit and satisfactory coefficient of determination. Retort temperature, speed of rotation, headspace and radius of rotation have a significant effect. Dimensional correlations were developed for convective heat transfer coefficient, in terms of Nusselt number as a function of Reynolds number, Prandtl number and relative headspace; the best agreement was obtained using the diameter of rotation as the characteristic dimension.     

TIME-VARIABLE RETORT TEMPERATURE PROFILES FOR CYLINDRICAL CANS: BATCH PROCESS TIME,ENERGY CONSUMPTION,and QUALITY RETENTION MODEL1

The batch retort model developed uses a heat transfer equation for heat conduction in cylindrical cans, first order kinetics for microbial inactivation, first order kinetics for quality losses and a transient energy balance to estimate steam consumption. For a given retort, lethality process and quality retention, the transient energy balance equation in the model allowed the identification of feasible time-temperature profiles reducing energy consumption, total process time or both. In the examples analyzed and depending upon product specifications, time-variable retort temperatures reduced process time by 18–55 min. These examples suggested that a change from constant to time-variable retort temperatures could increase canning capacity by 20–50%.     

HEAT TRANSFER RATES IN A CANNED FOOD MODEL AS INFLUENCED BY PROCESSING IN an END-OVER-END ROTARY STEAM/AIR RETORT

The effect of various factors on the heat transfer rates of a canned food model (gelatinized starch) were evaluated during thermal processing in an agitating retort. Process variables were retort temperature (110–130C), rotation speed (10–20 rpm), can headspace (6.4–12.8 mm) and starch concentration (3–4%). Thermal process parameters (heating rate index, f_h, and heating lag factor, j_ch) and the resulting process lethality, F_o and cook value, C_o were obtained from time-temperature data obtained during processing for three consecutive runs. Rheological properties and color were experimentally evaluated both before and after each run. Overall heat transfer coefficient (U_o) was calculated from the heating rate index using a lumped capacity approach. the study indicated that f_h, j_ch, F_o and C_o were influenced (P<0.05) by all process variables except can headspace. U_o was related to retort temperature, rotation speed and initial apparent viscosity. the best dimensionless correlation for U_o was Nusselt number (logarithmic scale) versus specific apparent viscosity and Froude number (R²= 0.65).     

基于断裂力学的立式杀菌锅全寿命疲劳分析

目的:研究一种新型立式杀菌锅在热机循环载荷下的疲劳强度,特别是在锅体出现裂纹后的剩余疲劳寿命以及影响杀菌锅疲劳裂纹扩展的因素.方法:从杀菌锅结构完好的设计疲劳寿命和有裂纹后的剩余疲劳寿命两个方面对其进行全寿命疲劳分析.采用Workbench分析杀菌和3种循环载荷下杀菌锅的力学特性;基于SGN曲线研究杀菌锅在3种交变应力下的设计疲劳寿命;基于断裂力学原理研究初始裂纹尺寸、压力、温度对有裂纹杀菌锅应力强度因子和剩余疲劳寿命的影响.结果:此类立式杀菌锅的设计疲劳寿命为5×10⁵次,满足设计需要且有一定安全余量;基于断裂力学分析得出杀菌锅裂纹尺寸寿命曲线,对含缺陷杀菌锅剩余寿命进行预测,具有一定创新性.结论:使用过程中应关注锅体内部裂纹的产生和扩展情况,可以根据试验提出的方法对杀菌锅裂纹缺陷进行强度分析和寿命预测.