Sunday, February 28, 2010

New Green-Concrete Process Combines Seawater, Flue Gas

(Las Vegas, Nevada) -- Cement scientist Brent Constantz wants concrete to be the
"hero" that cleans up dirty coal. "The reality is, coal is not going away," he says. "We
need to meet the world’s power demands without emitting more carbon." His answer? A
new type of concrete that sequesters carbon without disturbing its traditional binder:
portland cement.

This past summer, the Stanford University professor’s Los Gatos, Calif.-based startup,
Calera Corp., began making cement from flue gas and seawater at Dynegy’s gas-fired
1,500-MW Moss Landing Energy Facility. At first, Constantz hoped to replace portland
cement, which emits about one ton of carbon dioxide per ton produced. But after some
industry pushback and more research, he now says he can use Calera aggregate
synthetic stone, sand and gravel to capture CO2 and still produce net gains.

Constantz cemented the new course in Las Vegas on Feb. 3 appropriately, on the first
day of this year’s World of Concrete show speaking to 100 world-leading scientists and
engineers during a 90-minute seminar. In the packed room, Constantz, who owns more
than 70 patents for medical cement, assured the group that Calera could be used to
replace portland though it is not essential. "The way to get it accepted is probably
through the aggregate," he says. (In Las Vegas, Constantz said he can use aggregate
to store carbon in concrete.)
The pitch worked. Florian Barth, a structural engineer and incoming president of
American Concrete Institute, says Calera "has great potential." The seminar "was
promising," adds Steven Kosmatka, vice president of Skokie, Ill.-based Portland
Cement Association. "Although their process needs further refinement…we must keep
a careful watch on Calera," says another scientist who attended.

Unlike cement, aggregate is more voluminous in concrete, making up at least 75% of
the mix. "If we just replace the sand, we get to carbon-neutral," Constantz says. The
new route helps calm fears over using a new, synthetic binder. Kosmatka calls the new
approach a "home run." Barth adds that it could solve other industry problems. "It is
increasingly difficult to get mining permits," he notes.

Calera has gone from 10 employees last year to 100 today and is working on a pilot
plant on the East Coast. By 2010, it plans to have a factory cranking out its calcium and
magnesium carbonate.

Until now, technologies being developed for polluters center on underground carbon
capture and sequestration. CCS could offset 70 years of emissions, perhaps hundreds
more, according to the World Coal Institute. But Calera potentially has no shelf life as
long as the world builds with concrete, trapping up to a half-ton of CO2 in one ton of
material, Constantz says. At full scale, Moss Landing alone could trap 3.4-million tons
per year; that’s like putting over a million hybrids on the road, he adds.

As promising as it is, though, engineers want to see more data. "They have a long way
to go," Kosmatka says. "This is not something that people are going to be ordering next

By Tudor Van Hampton


Friday, February 19, 2010

History of a Dam

A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees (also known as dikes) are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are often used in conjunction with dams to provide clean electricity for millions of consumers.
The word dam can be traced back to Middle English,and before that, from Middle Dutch, as seen in the names of many old cities.

Most early dam building took place in Mesopotamia and the Middle East. Dams were used to control the water level, for Mesopotamia's weather affected the Tigris and Euphrates rivers, and could be quite unpredictable.

The earliest known dam is situated in Jawa, Jordan, 100 km northeast of the capital Amman. This gravity dam featured a 9 m high and 1 m wide stone wall, supported by a 50 m wide earth rampart. The structure is dated to 3000 BC. The Ancient Egyptian Sadd Al-Kafara at Wadi Al-Garawi, located about 25 kilometers south of Cairo, was 102 m long at its base and 87 m wide. The structure was built around 2800 or 2600 B.C. as a diversion dam for flood control, but was destroyed by heavy rain during construction or shortly afterwards.

The Romans were also great dam builders, with many examples such as the three Subiaco Dams on the river Anio in Italy. Many large dams also survive at Mérida in Spain (see List of Roman dams and reservoirs).

The oldest surviving and standing dam in the world is believed to be the Quatinah barrage in modern-day Syria. The dam is assumed to date back to the reign of the Egyptian Pharaoh Sethi (1319–1304 BC), and was enlarged in the Roman period and between 1934-38. It still supplies the city of Homs with water.

Eflatun Pınar is a Hittite dam and spring temple near Konya, Turkey. It's thought to the time of the Hittite empire between the 15th and 13 century BC.

The Kallanai is a massive dam of unhewn stone, over 300 meters long, 4.5 meters high and 20 meters (60 ft) wide, across the main stream of the Kaveri river in India. The basic structure dates to the 2nd century AD. The purpose of the dam was to divert the waters of the Kaveri across the fertile Delta region for irrigation via canals.

Du Jiang Yan is the oldest surviving irrigation system in China that included a dam that directed waterflow. It was finished in 251 B.C. A large earthen dam, made by the Prime Minister of Chu (state), Sunshu Ao, flooded a valley in modern-day northern Anhui province that created an enormous irrigation reservoir (62 miles in circumference), a reservoir that is still present today.

In Iran, bridge dams were used to provide hydropower through water wheels, which often powered water-raising mechanisms. The first was built in Dezful, which could raise 50 cubits of water for the water supply to all houses in the town. Also diversion dams were known. Milling dams were introduced which the Muslim engineers called the Pul-i-Bulaiti. The first was built at Shustar on the River Karun, Iran, and many of these were later built in other parts of the Islamic world. Water was conducted from the back of the dam through a large pipe to drive a water wheel and watermill. In the 10th century, Al-Muqaddasi described several dams in Persia. He reported that one in Ahwaz was more than 3,000 feet long, and that and it had many water-wheels raising the water into aqueducts through which it flowed into reservoirs of the city. Another one, the Band-i-Amir dam, provided irrigation for 300 villages.

In the Netherlands, a low-lying country, dams were often applied to block rivers in order to regulate the water level and to prevent the sea from entering the marsh lands. Such dams often marked the beginning of a town or city because it was easy to cross the river at such a place, and often gave rise to the respective place's names in Dutch. For instance the Dutch capital Amsterdam (old name Amstelredam) started with a dam through the river Amstel in the late 12th century, and Rotterdam started with a dam through the river Rotte, a minor tributary of the Nieuwe Maas. The central square of Amsterdam, covering the original place of the 800 year old dam, still carries the name Dam Square or simply the Dam.


Sunday, February 14, 2010

Moveable Bridge

A moveable bridge is a bridge that moves to allow passage for (usually) boats or barges. By making the bridge moveable it may be made low, which avoids the expense of high piers and long approaches, greatly reducing the cost of the bridge. The principal disadvantage is that the traffic on the bridge must be halted when it is opened for passages. For seldom used railroad bridges over busy channels the bridge may be left open and then closed for train passages. For small bridges bridge movement may be enabled without the need for an engine. Some bridges are operated by the users, especially those with a boat, others by a bridgeman, sometimes remotely using video-cameras and loudspeakers. Generally the bridges are powered by electric motors, whether operating winches, gearing, or hydraulic pistons. While moveable bridges in their entirety may be quite long, the length of the moveable portion is restricted by engineering and cost considerations to a few hundred feet.

There are often traffic lights for the road and water traffic, and moving barriers for the road traffic.

In the United States, regulations governing the operation of moveable bridges, for example, hours of operation and how much advance notice must be given by water traffic, are listed in title 33 of the Code of Federal Regulations; temporary deviations are published in the Coast Guard's Local Notice to Mariners.