奶粉中湿度检测方案(喷雾干燥机)

河北冀群仪器有限公司地址：河北省石家庄市裕华区翟营南大街29号电话：0311-68053182\83898812http：//www.jiqun-china.com传真：0311-68006320 英国 Labplant 喷雾干燥仪在奶粉中的应用 Labplant spray dryer tests The milk used was reconstituted in the following way： -200g milk powder 一1.7L of tap water giving 2L of milk with a measured density of 1.045 at 21’C. We used a fixed flow， whatever the experiment ； pump flow set at 5， corresponding to13.5mL/min. Varying the injection temperature of the product We did a first test with an injection temperature of 130’C and then a second test at 140'C.We saw that spray drying was achieved， apparently， comfortably at these twotemperatures.Effectively no liquid ran along the walls of the main spray chamber，even at130'C. This meant that we could work at 140’C or 130'C given the stipulated flow.In theory it is preferable to work at 140'C， because the higher the temperature the betterthe yield. We will try to prove this through our experiments. Varying the compressed air ratio /feed flow We worked with a flow set at 5 (13.5mL/min) and compressed air set at 3 bars(constant air inlet valve opening). In theory to increase the size of the agglomerate， it is necessary to favour the agglomerationmechanism over the drying process. One of the possible means is to decrease the sprayingrate. In the case of this equipment， to decrease the spraying rate you can either decrease theflow of compressed air through the injection nozzle (while keeping a constant pressure) oryou can decrease the pressure of the compressed air (while keeping a constant flow). Therefore we tried two tests with constant air and liquid flows， varying the pressure from 2to 3 bars. We observed the look of the powders we obtained ； it was difficult to decide justwith the naked eye， an additional granulometric(?) study would be necessary， but it did seem that the powder obtained with 3 bars of pressure was effectively finer than that obtained with2 bars. Research into the effective operational limits of the spray dryer We retained the same solution of reconstituted milk. At a given flow and pressure of air， we increased the flow of liquid from level 5(13.5mL/min) to level 10 (28.8mL/min). We very quickly saw that the formation of thespray in the atomisation tube was not good ： in effect the quantity of liquid going throughthe tube was too much and could not be vaporised on exiting the tube. This was why we hadsome liquid that ran out of the tube， ran along the walls of the spray chamber， of the fanchamber (cyclone?) and even in the recuperation chamber. Under these conditions the yieldof finished product would be bad. QUANTITATIVE STUDY The experiments carried out and the experiment details are given below. Experiment 1 ： starting from 100g/L of reconstituted milk Amount of water 1700g Volume of milk 2L Density of milk 1.045g/mL Humidity of milk 89.47 % mas Injection temp (??) 130'C Injection flow 13.5mL/min Working time 40 min Compressed air pressure 3 bars Humidity of labo 21.8%HR 6g vapour / m3 air Ventilator flow 70 m3/h Gas exit temp 77'C Air exit humidity 18.8%HR 21.3g vapour/m3 air Bottle size 339g Bottle+ wet milk 391.9 Bottle + dry milk 390 地址：河北省石家庄市裕华区翟营南大街29号 传真：0311-68006320 http：//www.jiqun-china.com From the experiment details we calculated the following： -humidity of the milk： 100 x water mass (water mass + powder mass) -numerical application ： % humidity of the milk= 100 x 1700/(1700+200)= approx 89.5% -the mass of the wet milk we collected=391.9-339=52.9g -the mass of the dry matter we collected=390-339=51g -humidity of the solid=100x(52.9-51)/52.9= approx 3.6% Materials‘balance sheet of the dry milk over the life of the experiment： -at the start ： dry matter is the result of the solution to be tested -at the exit： dry matter of the solid that was obtained Numerical application at the start ：13.5mL/min x 1.045 g/mL x 40 min x (100-89.47)/100= approx 59.4g at the exit：51g solid yield=100 x51/59.4= approx 85.9% Materials ‘balance sheet'of the water over the life of the experiment b)at the start ： (13.5mL/min x 1.045 g/mL x 40 min x 89.47/100)+70 m3/h x 6 g/m3x40/60=784.8 approx of water c))aat the exit ： (52.9g x3.6/100)+(70m3/hx 21.3 g/m3 x40/60)= approx 995.9 d)water yield= 100x 995.9/784.8= approx 127%