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Saturday, December 24, 2016

Chinese air pollution

I don't get it.  In-so-far as Chinese air pollution is caused by coal fired power stations, smelters and  other factory that spew out particulates and oxides of sulfur into the atmosphere, they could clean up the problem in a historical instant (say 2 years).  America did it and the technology is old hat.  In America the situation was dire.  Once the decision was made, it took them very little time  to stop all this nastiness going into the air.  The technology was patented in1907.

I can't help wondering what the motivation is of the Chinese government.  Is it ignorance.  Is it a lack of concern for their citizens.  Do they want their citizens to die young so they don't have to look after them in their old age.  What on earth is the problem.  They seem to be happy that a lot of their people are smoking so perhaps the last possibility is the correct one.  Anyway, technically, how would they do it.

For the particulates they install electrostatic precipitators.  Let me digress here and try to explain how they work.

Have you ever run a comb through dry air and then used the comb to pick up little pieces of paper from the table.  What is happening here?  When you rub almost any two different materials together, some electrons are rubbed off one on to the other.  If the rubbed materials are insulators, the electrons or lack of electrons stay on the surface of the two objects giving one a positive charge and one a negative charge.  Opposite charges attract and even a neutral object will be attracted to a charged one as some of the opposite charge on the neutral object is pulled toward the charged object.

Or have you ever shuffled your feet across a carpet and then walked over to a friend and brought a finger close to his ear.  A little spark jumps and so does your friend. You haven't sent much current to his ear but you were at a surprisingly high voltage which caused the spark to jump

Or have you ever got out of a car and as you went to close the door, you got a shock.  Once again a charged object sending a spark to an uncharged one.

In each case a charge has built up on the object and when you bring the charged object near to an uncharged object, electrons jump from the negative one to the positive one and neutralize the charge.  At a microscopic level, if you were a little charge particle, you would be pulled toward any nearby object which was neutral or had the opposite charge.

A lot of this is now done by electronic wizardry but I will describe it old school which is easier to understand.  You may have noticed that in older cars there is a coil.  Ask your granddad about them.  This is a transformer that has a few coils of wire coming from the battery and a lot of coils around it going to the spark plugs.  When a pulse of electricity is sent by the distributor from the battery through the primary (the few coils) it makes a magnetic field which cuts across the wires of the secondary.  This induces a voltage in the secondary.  How high the voltage is depends on the number of coils.  If there are ten times as many coils in the secondary as in the primary, the 12 volts of the primary (from the battery) will be stepped up 10 times to 120 volts. In a car the ratio of primary coils to secondary is much larger in order to get enough voltage to jump the gap in the spark plug.

In an electrostatic precipitator you have something similar except the voltage is stepped up to thousands of volts and you pass AC (alternating current) through the primary.  So far so good but useless.  You have also induced an alternating current in the secondary going positive and negative.  You need high voltage direct current.  No problem.  You rectify this alternating current with a wheatstone bridge.  Note that in the diagrams in the link they talk about resistors.  Replace then with diodes that only allow current to flow in one direction and you will understand rectification.  I'll leave you to puzzle this one out. It is rather neat.

You now have very high voltage Direct current.  You conduct this current to a bunch of spikes, plates or bars in the flu of the polluting chimney and electrons stream off  and attach themselves to the particles.  Once charged, they will be attracted to any neutral or positively charged material.  You then have only to pass this flu gas past, for instance, a wet, grounded surface and the particulates will glue themselves on to the water to be washed away.  Some precipitators are designed to collect the dry particles and shake them off.  Whichever system is used, problem solved.  Particulates removed.

The fine details are somewhat more complicated (aren't they always) but this technology can be bought off the shelf and with her command economy, I'm sure China can reverse engineer it and build a factory to turn these out in the thousands.

As for sulfur, have a look at this link.  Oxides of sulfur can also be removed and the technology is old.  One reason for doing this is  to recover the sulfur which is a valuable industrial feed material.  On the ecological side, oxides of sulfur in the atmosphere attract water and make aerosols of sulphuric acid which are both  toxic and corrosive.  With the recovered sulfur, the cost of a sulfur scrubber is negative (you make a profit on the process).

Incidentally, in a smelter, (factory where metal is recovered from an ore) an electrostatic precipitator also often recovers valuable materials so you often also make a profit on doing the right thing.

 What is wrong with the Chinese bosses.

There is a little wrinkle in this story, though.  Many scientists believe that the particulates in the atmosphere are shading the earth and keeping it cooler than it would otherwise be.  A fairly common estimate is about 2 degrees.  I don't know what proportion of aerosols (air born particulates) are due to Chinese factory pollution but for the sake of the argument, let's say a quarter.  If the Chinese did clean up their pollution, and if the estimates are correct, we could expect a sudden jump of half a degree (centigrade) in our atmospheric temperature.

We should see the results of this experiment fairly soon.  The Chinese population is getting fed up with being slowly poisoned by their leaders who are sitting on their hands.

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