. 15 .
国际造纸 2008年 第27卷 第1期
前沿
.
热点
Front
.
Focus
different pH, temperature, concentration
and chemical composition. Reactions
may be partly meaningful with targeted
results, but partly reactions are generated
randomly, uncontrolled and by accident
resulting to unwanted outcome.
Several circulating loops of the PM
short circulation process will keep part of
chemicals in circulation longer periods
thus extending the time with above,
explained effectly. The fi gure 1 shows the
circulating loops and fi rst pass percentage
of additive fl ows to the slice.
If additive is added into the mixing
chest, approx. only 50% of the fl ow has straight access as a fi rst pass
fl ow to headbox and as much as 50% of the fl ow begins to re-circulate
in loops. The long delay time with circulations slows down and makes
it more diffi cult to make production adjustments. The extended delay
time, multiple re-circulations of partial fl ows makes the whole process
complex. Chemical reactions and the wet end surface chemistry is
diffi cult to predict and follow - specially in situations when the process
is not well balanced. System cleanliness also can be widely reduced
due to these facts. The process can generate deposits in uncontrolled
situations.
1.1
Slow blending versus fast and effective mixing of additives
If mixing of reactive additive into a complex process media
is made with a fast and effective manner, outcome is a reaction
or reactions with the correct manner and with targeted end result.
Reaction is R + K
→ AB. Only small number of side effects may
come up.
If mixing is made slowly and with a random interaction and
concentrations, result is that the injected additive will meet varying
conditions on its way forward in the process. There can be several
different reactions:
R + H
→ YV;R + K → AB;R + YV → LKJ;YV + AB → ED.
Extended time and random additive concentrations bring
possibilities for additional unwanted side reactions.The background
and problems can be summarized as follows:
-dosage points of additives vary from mixing chest to headbox
feed pipe
-circulating loops distribute additives across the process with
large variation of time delay
-addition points are located early in the process to
“guarantee”
decent mixing
-additives have a long delay in the process before sheet
formation
-long response times in dosing adjustments and control
-strong beliefs exist about
“right” dosage locations
-complex chemistry
-high additive consumption
温度、浓度以及化学品消耗量
注入工艺过程，反应效果可能
只是预期效果的一部分，这仅
有的一部分也只是意外产生的、
随机的、失控的、并不期望的
结果。
由于上述滞留造成化学品
在上浆系统的各个回路都有一
定的滞留。图 1 所示为各个回
路添加剂的单程通过百分率。
如果添加剂在混合池加入，
单程通过量只有 50%，或者说只有 50% 的添加剂直
接到达了流浆箱，其余 50% 的添加剂在系统中循环，
延时越长系统生产调节越困难，延时时间加倍了再循
环药品的量，使工艺系统成分复杂化，湿部化学品反
应平衡越来越难以预料，难以控制，难以追踪。特别
是在系统平衡还没有完全达到时，这种无序状态会产
生大量失控垃圾，使系统的清洁度大大降低。
1.1
添加剂的缓慢混合与快速高效混合的比较
如果添加剂以快速高效的方式混合到复杂的系统
中，反应的结论是混合的方式正确，可达到预期效果，
例如：R + K → AB。
如果混合在缓慢且伴随有随机交互作用和浓度变
化，结论是注射的添加剂在工艺系统的进程中遇到了
各种不同的条件产生了多种可能的效果 :
R + H
→ YV
R + K
→ AB
R + YV
→ LKJ
YV + AB
→ ED
延时和随机浓度带来了一些有害的边缘反应 :
-
添加剂的计量点从混合池到流浆箱喂料管之间
变化
-
循环回路中化学添加剂的分配随时间延时变化大
-
增加早期加入点以“保证”完全混合
-
添加剂在纸张成形之前已在工艺过程中长时间
滞留
-
计量调整以及控制的响应时间长
-
坚信现有的就是“正确的”
-
化学复杂化
-
添加剂消耗量增高
-
结果可预见性低
-
产生沉积的风险大
Figure 1 PM short circulation process
图 1 纸机短循环工艺
Deacration /
Deculator
3.
15%
20%
4.
5.
5%
10%
10%
2.
1.
３.
Addition point and single pass%:
1.Machine&mixing chest 50%
2.Before mixing pump 55%
3.Before Deculator 73%
4.Before headbox screen 86%
5.Before headbox 90%