“Be kind, for everyone you meet is fighting a hard battle” - Often attributed to Plato but likely from Ian McLaren (pseudonym of Reverend John Watson)

Friday, July 03, 2009

Energy use in construction in China

I've been fortunate enough to have spent almost two weeks in China. I spent four days in Beijing, four days in Xi' An, three in Kunming, and most of a day in Guangzhou. I was there as part of a People to People Citizen Ambassador Program with a Public Works delegation. As such, the concentration during the professional meetings revolved around public works and we met with highway and traffic engineering groups, wastewater treatment facilities managers and engineers, and "underground" (known in the U.S. as subway) engineers.

We also had several cultural opportunities and were fortunate enough to visit many of the premier Chinese cultural sites, such as Tian An Men Square, the Forbidden City, the Great Wall, and the Terracotta Warriors. I felt privileged to visit these amazing sites, but the most compelling memories I'll keep are related to the openness of the people. We talked about politics, about Chairman Mao (60% good, 40% bad according to one of the people I spoke with in depth), the Cultural Revolution, local, regional, national, and global politics. I believe I got at least a rudimentary understanding of how the Chinese people (though certainly not the Government) feel about their place in the world, both historically and currently.

But one of the very most stunning things was the construction activity in China. In every city we visited, there were literally hundreds of tower cranes erecting massive structures. The vast majority of the structures were concrete, and I got curious about the consequent energy usage and greenhouse gas emissions. Per Wikipedia (and consequently unarguably) it takes anywhere from three to six gigajoules of energy to produce a tonne of cement. I think, based on my observations, that China would be at the high end of this range, so I'll go with six. This is is about 2.72*10^6 joules per pound. A sack of cement contains 94 pounds, and a garden variety concrete mix might use about 6.7 sacks of cement per cubic yard. So, just the cement in a cubic yard of concrete requires 6.7*94*2.72*10^6 or 1.71*10^9 joules of energy to produce. This is the total heat energy available in about 14 gallons of gasoline. It takes no account of the aggregate, the sand, the water, and the admixtures, nor of the other construction materials utilized.

Further, the production of cement is a "double whammy" with respect to carbon dioxide emissions. Not only is it extremely energy intensive, but the fundamental process of cement production is to "calcine" limestone, that is, to take limestone (calcium carbonate, CaCO3) and use heat to turn this limestone to lime (CaO), releasing CO2 in the process. One of the goals of my China adventure is to find a way to work with the Chinese to produce cementitious materials with a reduced cement content and thus reduce the CO2 impact of concrete construction.

In any case, the graphic above (courtesy of Prof. Goose at The Oil Drum) shows Chinese cement production in 2007 at 1.3*10^9 metric tonnes (1.3 "gigatonnes"). Using the energy input estimate from above, this would involve about 7.8*10^18 joules. This amount of energy in a year is an average power (easily found using WolframAlpha) of 2.47*10^11 watts.

This is a staggering rate of energy use. Typing "7.8*10^18 joules/year in watts" into WolframAlpha yields not only the above number for power but shows that this about 1.9% of the rate of global power consumption. And this is just to make cement, not the power required from limestone quarrying through placing concrete into a structure, let alone all of the other components comprising a completed structure.

Using a variety of approximations and estimates for the amount of "space" this quantity of cement could be used to produce, and the embedded energy in building construction (see here), I estimate that overall energy use in concrete framed construction in China in 2007 was on the order of 3.8*10^19 joules. This is getting to be a very significant portion of world energy usage, on the order of 9%. It's also over 40% of China's total energy usage. This would seem to be the real "Great Leap Forward," but how long can it last?

1 comment:

Matt Hux said...

There is an ongoing joke in China. The new state bird is called the "crane." You were able to experience this through all of the construction.