关键词：
工厂化水产养殖;pH;自动控制;比例微积分控制;电磁阀
摘 要：
根据鱼类养殖的水体适合pH值范围为6.5～8.5,硝化细菌进行硝化反应去除氨氮的pH值在7.0以上,养殖水体的pH值大于8.75就会产生大量对鱼类有毒的非离子态氨的生产实际情况,进行了工厂化水产养殖水体的pH值控制研究。由于pH值的中和过程是非线性的,很难控制,所以本文根据水产水体养殖的要求确定将pH值控制在7.0～7.5之间的稳定范围内,确保整个控制过程在pH值变化的线性范围,降低控制难度。控制采用PID算法,以占空比方式控制电磁阀添加中和剂,实现对pH值的控制。中和剂选择NaOH和NaHCO3,并进行了稳定控制配比试验,浓度分别为2g.L-1和20g.L-1的配比组,获得满意效果。本控制系统使用电磁阀而不是变频器或是调节阀之类昂贵作为执行元件,方法简单,成本低廉,控制准确可靠,是一种非常适用于工厂化水产养殖的pH值在线自动控制系统。
译 名：
Automatic control system of pH value in the recirculating aquaculture
作 者：
ZHU Ming-rui1,2,CAO Guang-bin1,JIANG Shu-yi1,HAN Shi-cheng1(1.Heilongjiang River Fishery Institute of Chinese Academy of Fishery Science,Harbin 150070,China;2.Collage of Engineering,Shanghai Fisheries University,Shanghai 200090,China)
关键词：
industrialized aquaculture;pH;automatic control;PID;electromagnetic valve
摘 要：
Fish generally can tolerate a pH range from 6.5 to 8.5.The recirculating aquaculture system always depends on nitrifying bacteria to transform toxic ammonia into nitrate-nitrogen,and this transformation process will reduce the pH of culture water.When the value of pH is below 7,the activity of nitrifying bacteria will be decreased.If the value of pH is below 6,the nitrifying bacteria will be inhibited and do not remove toxic nitrogen wastes.The value of pH affects ammonia form in water.At a pH of 7.0,most of total ammonia are in the ionized form,while at a pH of 8.75,up to 30 percent of total ammonia are in the un-ionized form.The un-ionized form of ammonia is extremely toxic to most fish.The optimum pH range for recirculating aquaculture system should be from 7 to 7.5 and it's necessary to monitor and control the value of pH in the industrialized culture water.Though the pH auto control system is used widely in industry and environment field,there is no effective pH control system applied to industrialized aquaculture.The pH control is recognized as one of the most difficult problems in the process control field because of its highly nonlinear nature.In the recirculating aquaculture system,because the optimum variation of pH is a very small range from 7 to 7.5,it can be considered as a linear parameter.As the pH of culture water decline gently,electromagnetic valve was chosen as control element.Based on the experience of the pH control in industry and environment field,we used PID arithmetic to control electromagnetic valve with the method of duty ratio to add chemical neutralization solution,which was mixed by sodium hydroxide and sodium bicarbonate,so that we built a pH on-line auto control system which could meet the needs of pH control in recirculating aquaculture water.For controlling the pH of aquaculture water,the most commonly used buffers are sodium bicarbonate and calcium carbonate,but calcium hydroxide,calcium oxide,and sodium hydroxide have also been used.In this system,we used sodium hydroxide and sodium bicarbonate as neutralization solution.According to the experiment we found that sodium hydroxide changed pH very quickly,but it could not increase alkalinity as to cause electromagnetic valve to work so frequently that its life-span decreased greatly.Adding sodium bicarbonate could maintain culture water in the zone of high alkalinity and electromagnetic valve did not run frequently.Usually,the addition of sodium bicarbonate at a rate of 17 to 20 percent of the daily feeding rate is sufficient to maintain pH and alkalinity.Actually,it was difficult to meet the needs of pH and dosage of sodium bicarbonate at same time when we used sodium bicarbonate solely.So we used sodium hydroxide and sodium bicarbonate together.Considering all factors such as pH,alkalinity,the dosage of the neutralization solution and life-span of electromagnetic valve,the concentrations of the sodium hydroxide and sodium bicarbonate were determined as 2 g·L-1 and 19.6 g·L-1,respectively.The parameters of PID which controlled sodium hydroxide were Kp=4,Ti=240 s,Td=30 s and the parameters of PID which controlled sodium bicarbonate were Kp=6.5,Ti=120 s,Td=30 s.Because of using electromagnetic valve,the cost of this system was much lower than other pH auto control systems and this kind of pH control was suitable to recirculating aquiculture system.
