Energy use in the production of paper towels

Cecil's Columns/Staff Reports
1

In this column Cecil cites our own Una Persson to prove that paper towels use more energy than electrical hand blowers. No offense meant, wouldn’t it have been just as easy to cite her actual calculations rather than her not inconsiderable authority? I’ve seen this factoid bandied about in the past, and in most of the calculations they assume that virgin bleached fiber is used to produce paper, but fail to take into consideration the energy produced during the recovery process.

From this cite there is a total electrical production of 655 kWh of electricity per air dry ton (ADT) of pulp produced. The actual pulping processes consume less than this amount, so pulp mills are net exporters of energy, generating 17 kWh net energy per ADT of pulp. This applies to bleached white pulp.

If the pulp produced is the unbleached kraft pulp like that used in most hand towels the net electrical production is an additional 175 kWh/ADT. Look at Table I in the linked cite and you can deduct the amount used on oxygen delignification and bleaching. In that case you would generate slightly less energy because O2 delig produces dissolved wood for the boilers, but the energy penalty is miniscule compared to the 175 kWh/ADT saved.

Paper making would use more energy than the 141 kWh/ADT than listed for the pulp machine, but most mills are integrated, so you wouldn’t have to have both, just one or the other.

I agree that all paper mills have power generation equipment using wood waste, coal, or natural gas, and sometimes all three, switching from one to the other as the price of each fluctuates. I’m just questioning what the calculations show for the net energy consumption of an integrated mill producing hand towels. As Una knows quite well, in engineering it’s often a question about where to draw the box. I just want to make sure it’s drawn in the right place.

Now, if you were talking about fine papers, bleached to 94 ISO brightness and coated to a fare thee well, that would be different, but nobody dries their hands with stationary.

2

I have limited time online in the next week, but I feel I should give you some more information to consider.

Cecil has but 800 words per week to fit his column into, and he writes for an audience which, while smarter than most, is largely non-technical. As a result, sometimes detailed calculations are not spelled out in the articles.

Your skepticism is good - but note as well that Cecil does not just rely on any one person for his analyses. He has other fact-checkers available to cross-check consumptions and sources as well, as I can attest due to some errors they found in some of my initial calculations. Cecil rarely, if ever, relies on just a single source of info.

From your own cite, going forward a little bit, one can see that newsprint paper (as an example of a “rougher” paper) takes an energy of 2840 kWh/ADt for TMP, and 790 kWh/ADt for DIP (recycled), and using an 80/20 ratio you get about 2430 kWh/ADt. However, I looked at a large number of sources, as well as talked to personnel at a paper company who I’ve worked for which makes both paper towels and cardboard (who would not give me exact numbers, but who said that 2430 kWh/ADt was “in the ballpark” for towels as well, but for a “good-running, modern mill” - of course the sad thing is, many mills are not running at near the efficiency they actually should, due to the cheapness of power. The Canadian paper you cite, which was actually one of the first ones I read in helping to investigate this, is referring to a “modern” mill in what I and others were assuming was a relatively new condition.), and ended up with a range of energy production values from a low of 1800 kWh/ADt to a high of 8204 kWh/ADt (assumed corrugated, unbleached paper, so not totally the same thing). What I did was a sensitivity analysis over a range of assumed paper energy consumptions. Note as well that many sites online claim to include the logging, transport, transloading, hogging, and other costs including waste and effluent disposal, which likely explains the large ranges. I tried to dig into what the breakdown was for the harvesting to chipping process was, spending a very large amount of time talking to renewable energy folks and reading USFS papers, but was unable to come up with a number I felt confident of using. Depending upon the State, location, and type of wood source, the renewable energy supply coordinators I worked with gave me appallingly large differences from “best case” to “worst case” cost and energy consumption. I don’t recall the numbers per hogged ton of wood chips, but the ratio was along the lines of 10:1.

Operation times for conventional dryers range from 15 seconds to 60 seconds, and there are about 3 standard power outputs, so as a result there was about a 1:3 difference in power consumed while running. So I graphed the possible ranges of power consumption from those cases. In each case, I took the most likely case which I judged, and compared the two.

My sheet has several things in it which it tries to take into account, including the transport energy of the new paper, the disposal energy of wet/used paper, etc., including some possibly proprietary info, but I can run a few quick numbers. For an example, if we assume a 1.5kW dryer at 20 seconds cycle time, then the break-even for the paper case is about 1127 kWh/ADt. The outlier of course was the Dyson - if you can accept the level of drying achievable from it, its power consumption is very low. The break-even in terms of the paper case is then reduced to 748 kWh/ADt.

That’s about all I can say right now on this.

3

Note that when I said:

I meant just the 8204 kWh/ADt value, not all the values.

4

In the case of the thermomechanical pulp cited, I certainly believe the energy usage is high. TMP is groundwood, in which mechanical and thermal energy is used to break up wood into fiber. It is an energy hog because it operates in yields so high that there is no energy produced in the recovery boilers, in fact, there are no recovery boilers. It’s cheaper in wood cost, everything’s a tradeoff. The company I work for is no longer in the groundwood business for various reasons, but the cost of energy is among them.

However, I would like to leave you with this The value of electrical energy is around $0.12 per kWh. I know this is more than the cost of production, but if you can’t get 12 cents worth of value out of using it you would sell it instead of using it to make paper.

If we were at the 1127 kWh/ADT break even price that means the electrical cost of a ton of paper is $170. The August 14th price for NBSK (Northern Bleached Softwood Kraft) was only $830/ADMT, or $753/ADT. I promise you that if it took $180 worth of electricity to make $750 worth of pulp not a paper company in the world would be in business.

Up to the headbox of the paper machine, the largest single cost of paper production is the cost of fiber, purchasing trees. Following that comes labor, or labour for the Anglophiles, with energy either third, or fourth, depending on how old the mill is and whether you’ve recovered the capital invested or have to amortize the cost of equipment, which is ruinously high. A new pulp mill in a size large enough to be economically feasible to run would cost in the neighborhood of $1.5 billion. The “b” is not a typo.

Chemicals are in there as well, but most pulping chemicals are recovered, with soda losses being on the order of 20 pounds per ADT, and most of the energy cost of bleaching, which is already accounted for, is in the generation of chlorine dioxide on site.

Paper mills work hard on saving energy, because the marginal cost of power can make or break an operation. Try to find a paper mill in the Pacific Northwest lately. Those high electric prices combined with high wood costs drove them all out of business.

Anyway, my point, and I do have one, is that electrical costs are much lower than I have seen calculated, and without revealing proprietary information, I can safely say that net energy consumption for brown kraft paper towels is much less than the 1127 kWh/ADT.

5

I couldn’t tell in the column whether you took the energy of production for the actual machinery into production (as in, the blow dryer & the paper towel holder.) I know those values would vary even more, but of course, the blow dryer would take much more energy to produce than what is essentially a plastic box.

6

I tried to take those into account, although there are a lot of variables depending upon the blower and the assumptions for the raw materials production. See the other thread for more a couple more details.

7

I used to work in an ad agency, and one of the clients was a marketer of paper collars used by barbers to keep customers’ hair from falling down their necks.

I swear to God, the owner’s basic directive to us was, “Do a good job advertising for me - but not too good.” You see, he didn’t want to offend the cloth towel people who, uh, were usually mobbed up.

We also pushed the client’s paper towels, too, and the only product lines we could take shots at were the electric hand driers to the effect that the hot air inlet originally comes from a hole at the base of the bathroom wall itself!!!

Thus the threat was: you’re customers are drying their hands with dirty air which, by the way, is also contaminated with shit molecules from the nearby row of toilet bowls.

I never did establish the legitimacy of those claims, but they were never challenged. Maybe the electric hand drier folks thought my guy was mobbed
up :smiley: :smiley: :smiley:

8

Why not just shake your hands and wait a few minutes? That requires 0 artificially produced energy (I’m not counting the energy required to shake your hands as “artificial”).

9

Right. Stand around a public washroom shaking your hands dry.

After a minute or two, wipe 'em at the crotch of your pants. Who’ll notice? :smiley: :smiley: :smiley:

10

The continous cloth towel things aren’t very common around here. They’re not an option for me, I’ll use my pants or shirt first.