热电厂集中供热——过热蒸汽在轮胎工业中的应用

阐述了热电厂集中供热提供过热蒸汽在轮胎工业中的应用,根据轮胎双模定型硫化机的硫化工艺要求,实际采用内温和外温的供汽参数和供汽方案,以及过热蒸汽减温、减压装置控制原理。     

热电厂集中供热——过热蒸汽在轮胎工业中的应用

阐述了热电厂集中供热提供过热蒸汽在轮胎工业中的应用,根据轮胎双模定型硫化机的硫化工艺要求,实际采用内温和外温的供汽参数和供汽方案,以及过热蒸汽减温、减压装置控制原理。     

1GW超超临界机组主汽温控制策略的仿真

对谏壁电厂1GW超超临界机组主汽温控制的过热汽温控制系统运用改进的Smith预估控制实现,有效地解决了超超临界机组的大延迟和大惯性问题.AnySimu仿真结果表明,改进的Smith预估补偿控制策略消除了主汽温控制过程中的惰性区,控制回路的调节速度加快,具有较好的控制性能.     

金桥热电厂过热汽温控制系统分析及优化

通过增加燃烧量前馈、主汽压力前馈、摆动燃烧器前馈和4阶惯性减温器后汽温前馈,克服了过热蒸汽温度因机组负荷变化、燃料量变化、炉膛火焰中心变化等因素造成的扰动,解决了过热蒸汽温度系统原来存在的问题,取得了良好的控制特性。     

基于ADRC-PID的超临界机组主汽温控制系统设计

针对超临界机组动态特性复杂、变参数的运行方式、多变量的控制特点,提出二级过热汽温主调节器采用自抗扰控制器(ADRC),副调节器采用PID控制的设计方法,从而构成ADRC-PID方法来控制超临界主汽温.同时采用600MW超临界机组为被控对象进行试验研究.试验结果表明,用ADRC-PID控制主汽温对被控对象模型的不确定性和...     

锅炉过热蒸汽减温器的设计计算分析

过热器在蒸汽锅炉上已被广泛使用。保证过热蒸汽温度在不同负荷、不同工况下接近恒定,就必须采用汽温调节装置。目前国内外多采用喷水式或表面式蒸汽减温器。汽温调节器的良好设计不单与锅炉运行的安全性、经济性有关,同时与汽温调节的自动化有密切关系。     

基于规则自寻优的过热汽温模糊控制

针对过热汽温大惯性、大延迟的动态特性及在电厂单元机组中的控制难点,根据规则自调整模糊控制算法,同时考虑误差和误差变化率对模糊控制的影响,采用全论域自修正因子函数实现了改进的模糊PID复合控制。同时在误差较小时设置阈值细调自修正因子,大大增加了系统的稳定性。仿真结果验证了该控制方法的有效性,对过热汽温的控制有一定的指导意义。     

锅炉汽包水位的控制与调整

汽包水位是锅炉运行中的一个重要监控参数,它反映了锅炉负荷与给水的平衡关系。汽包水位过高会造成汽空间缩小,将会引起蒸汽带水,影响汽水分离效果使蒸汽品质恶化,以致在过热器管内产生盐垢沉积,使管子过热,金属强度降低而发生爆破。水位过低会造成锅炉水循环的破坏,使水冷壁管超温过热。因此加强对水位的控制和调整至关重要。这就要求汽包水位在一定范围内,适应各种工况的运行。     

分数阶控制器在过热汽温控制中的应用研究

在传统串级控制基础上结合分数阶PIλ Dμ控制器,提出过热汽温的分数阶PIλDμ串级控制策略.采用粒子群优化算法对分数阶PIλ Dμ控制器参数进行整定.在Matlab/Simulink仿真环境中对分数阶PIλDμ控制器和整数阶PID控制器的控制效果进行仿真对比,结果表明分数阶pIλ Dμ控制器在设定值跟踪、扰动抑制和鲁...     

尼龙66聚合反应器排汽回收利用技术改造

介绍了尼龙66连续聚合纺丝生产工艺路线,改造前反应器排放大量的过热蒸汽直接进入大气,造成能源浪费和环境污染。通过技术改造,新增饱和蒸汽塔、过滤器等废汽回收利用装置,根据高压蒸汽减温减压装置原理,将反应器排放的1.85 MPa,245℃过热蒸汽在饱和塔内进行喷淋,经过滤器除杂转换为0.8~1.0 MPa饱和蒸汽,作为浓缩槽热源;浓缩槽排放蒸汽的余热改造后作为第三温水系统和冬季取暖的热源,排汽余热得到充分利用。运行过程中,通过稳定控制反应器压力、保持反应器排汽阀的喷淋水流量和压力稳定等工艺条件,定期清理疏水阀等,可有效预防管路和设备堵塞。改造后,装置运行稳定,能耗降低,尼龙66聚合物相对黏度的均匀性和原丝一等品率均有所提高。     

Production of furfural from agricultural wastes by using pressurised water in a batch reactor

Agricultural wastes such as rice husks and sawdust can be used for the manufacture of chemicals including furfural and acetic acid. In the present work the conventional use of superheated steam has been replaced by the use of superheated water in the acidic hydrolysis of rice husk and sawdust. Comparable yields of furfural have been obtained by using superheated water in place of superheated steam in the same temperature and pressure range. This is an attempt to economise the heat requirement and reduce the cost of production of furfural.     

Controllability of Product Moisture Content When Nonscreened Sawdust Is Dried in a Spouted Bed

The control of the dried product's moisture content is of importance in the production of fuel pellets. Tests have been made in air and superheated steam in a spouted bed using the outlet temperature of the drying medium as a control parameter of the dried material's moisture content. For superheated steam different settings for the inlet medium temperature are also used. In the moisture content interval of 8-17% wet base there is a linear correlation between the dried material moisture content and the outlet temperature of the drying medium. When drying nonscreened sawdust in a spouted bed it is recommendable to use the outlet temperature of the drying medium as a control parameter of the dried material moisture content. This is independent of the size of the sawdust, whether superheated steam or air is used as a drying medium.     

基于Aspen Plus的焦炉气制甲烷工艺模拟与分析

利用Aspen Plus模拟软件对焦炉煤气制甲烷工艺进行了流程模拟。分析了甲烷化反应压力、过热蒸汽与反应进料气质量比对反应器出口温度和甲烷产量的影响。结果显示,当反应压力在10×103kPa³0×103kPa时,可调控两个反应器出口温度范围均为0℃30×103kPa时,可调控两个反应器出口温度范围均为0℃⁵0℃,甲烷产量变化很大;当过热蒸汽与反应进料气质量比在0.0550℃,甲烷产量变化很大;当过热蒸汽与反应进料气质量比在0.05⁰.40时,可调控第一、二级反应器出口温度范围分别为0℃0.40时,可调控第一、二级反应器出口温度范围分别为0℃⁵0℃和0℃50℃和0℃²5℃,甲烷产量变化不大。     

DRYING RATE AND TEMPERATURE PROFILE FOR SUPERHEATED STEAM VACUUM DRYING AND MOIST AIR DRYING OF SOFTWOOD LUMBER

Two charges of green radiata pine sapwood lumber were dried, either using superheated steam under vacuum (90°C, 0.2 bar abs.) or conventionally using hot moist air (90/60°C). Due to low density of the drying medium under vacuum, the circulation velocity used was 10 m/s for superheated steam drying and 5.0 m/s for moist air drying, and in both cases, the flow was unidirectional. In drying, stack drying rate and wood temperatures were measured to examine the differences between the superheated steam drying and drying using hot moist air.

The experimental results have shown that the stack edge board in superheated steam drying dried faster than in the hot moist air drying. Once again due to the low density of the steam under vacuum, a prolonged maximum temperature drop across load (TDAL) was observed in the superheated steam drying, however, the whole stack dried slower and the final moisture content distribution was more variable than for conventional hot moist air drying. Wood temperatures in superheated steam drying were lower.     

DRYING RATE AND TEMPERATURE PROFILE FOR SUPERHEATED STEAM VACUUM DRYING AND MOIST AIR DRYING OF SOFTWOOD LUMBER

Abstract

Two charges of green radiata pine sapwood lumber were dried, either using superheated steam under vacuum (90°C, 0.2 bar abs.) or conventionally using hot moist air (90/60°C). Due to low density of the drying medium under vacuum, the circulation velocity used was 10 m/s for superheated steam drying and 5.0 m/s for moist air drying, and in both cases, the flow was unidirectional. In drying, stack drying rate and wood temperatures were measured to examine the differences between the superheated steam drying and drying using hot moist air.

The experimental results have shown that the stack edge board in superheated steam drying dried faster than in the hot moist air drying. Once again due to the low density of the steam under vacuum, a prolonged maximum temperature drop across load (TDAL) was observed in the superheated steam drying, however, the whole stack dried slower and the final moisture content distribution was more variable than for conventional hot moist air drying. Wood temperatures in superheated steam drying were lower.     

COMPARISON OF SUPERHEATED STEAM AND AIR OPERATED SPRAY DRYERS USING COMPUTATIONAL FLUID DYNAMICS.

In this paper a numerical simulation of a spray dryer using the computational fluid dynamics (CFD) code Fluent is described. This simulation is based on a discrete droplet model and solve the partial differential equations of momentum, heat and mass conservation for both gas and dispersed phase.

The model is used to simulate the behaviour of a pilot scale spray dryer operated with two drying media : superheated steam and air Considering that there is no risk of powder ignition in superheated steam, we choosed a rather high inlet temperature (973 K). For the simulation, drop size spectrum is represented by 6 discrete droplets diameters, fitting to an experimental droplets size distribution and all droplets are injected at the same velocity, equal to the calculated velocity of the liquid sheet at the nozzle orifice.

It is showed that the model can evaluate the most important features of a spray dryer : temperature distribution inside the chamber, velocity of gas, droplets trajectories as well as deposits on the walls. The model predicts a fast down flowing core jet surrounded by a large recirculation zone. Using superheated steam or air as a drying medium shows only slight differences in flow patterns. Except for the recirculation which is tighter in steam.

The general behaviour of droplets in air or steam are quite the same : smallest droplets are entrained by the central core and largest ones are taken into the recirculation zone. In superheated steam, the droplets penetrate to a greater extent in the recirculation zone. Also, they evaporate faster. The contours of gas temperature reflect these differences as these two aspects are strongly coupled. In both air and steam there is a “cool” zone which is narrower in steam than in air. Finally, the panicle deposit problem seems to be more pronounced in air than in steam.

Adding to the inherent interest in using superheated steam as a drying medium, the model predicts attractive behaviour for spray drying with superheated steam. In particular. under the conditions tested with the model, a higher volumetric drying rate is obtained in superheated steam.     

CMAC—PID复合控制在焦炉加热中的应用

针对焦炉加热的大惯性、大滞后和时变性的特点,采用小脑神经网络CMAC和PID复合控制相结合,将此方法应用在焦炉加热中,并进行了仿真研究。仿真结果表明,这种方案对控制系统具有较强的鲁棒性和良好的调节性能,提高了系统的动静态性能指标。     

Inversion Temperature and Pinch Analysis,Ways to Thermally Optimize Drying Processes

This work studies the compatibility and suitability of a combined inversion temperature and pinch analysis with the process selection for air and superheated steam spray drying of milk solids. The inversion temperature is a good starting point for an energy analysis because it is a simplified rate-based approach to comparing the steam and air drying systems. pinch analysis enables process integration, at least on a heat recovery and heat exchanger network level.

The resulting inversion temperature for the studied system was estimated as 182°C for the dryer inlet temperature. However, mass and energy balances showed that a minimum inlet temperature for spray drying of 184°C was required for the superheated steam dryer in order to ensure that the outlet solids temperature above the dew point temperature.

The inversion temperature is still very relevant in the early stages of a design process because it allows a quick assessment of which drying medium should result in a smaller dryer. It was evident that the steam system is better from an energy perspective because of the recoverable latent heat of the water vapor carried out of the dryer with the recycled steam. The steam system has between 82 and 92% of thermal energy recovery potential as condensable steam, compared with 13–30% energy recovery of the air system. However, other important design and operational factors are not discussed here in detail.

Combining the inversion temperature and pinch analysis suggests that superheated steam drying both gives better energy recovery and is likely to give smaller dryers for all operational conditions.