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Changes in the trunk

Vehicles adapted to natural gas get lighter tanks and with different formats

A new phase in the history of natural gas for automobiles is beginning in Natal, in the state of Rio Grande do Norte. The promise is made by researchers from the Gas Technology Center (CTGás), an institution that came from a partnership between Petrobras and the National Industry Service (Senai). There is one project that promises to eliminate one of the headaches of the owners of cars with this kind of fuel: the huge and heavy cylinder installed in the trunk of the vehicles, to hold the natural gas for vehicles (NG). There are about 350,000 automobiles or light trucks in Brazil with the problem, which is still a small number, accounting for 1% of the 34 million total fleet.

These cars have the normal tank for storing liquid fuel (gasoline or alcohol), plus a cylinder for the gas. If CTGás can help it, this inconvenience will shortly cease to exist. The cylinders should be smaller and lighter and, best of all, are going to be adapted to the format of the empty spaces there are beneath the vehicle, around the spare tire or in the roof. For the time being, many of these formats are still being kept in secret, because the institution will be depositing patents for the new geometries of the tanks with the National Institute of Industrial Property (INPI) by the end of the year. The researchers believe that in two years at the most these new products will be on the market at a competitive price.

The new designs will be possible with a drastic reduction in the pressure used for storing the GN. The current cylinders have steel walls from 2 to 3 centimeters thick, to withstand the high pressure of the gas, held at 200 bars (just remember that the pressure at sea level is 1 bar on average). At this pressure, the molecules of gas become “squeezed” inside the cylinder. At the service station, natural gas reaches a pressure that varies from 6 to 10 bars. With these lower pressures, and high dispersion of the molecules, it would not be possible to push inside the cylinder the 17 cubic meters of gas that are sufficient to give the vehicle an autonomy of 200 kilometers.

Reducing the pressure of the gas without cutting the number of kilometers covered is the challenge for the engineers from CTGás, which is part of the National Network of Natural Gas Technology Nuclei (Regás), made up of units from Senai, which intends to contribute toward a greater participation of natural gas in industry and in other branches of economic activity. The researches, which began three years ago, are financed by the Financier of Studies and Projects (Finep) and by the Gas Energy Network, made up of Petrobras and the Brazilian Bolivia-Brazil Gas Pipeline Transport Company. The studies are based on the phenomenon known as adsorption, in which molecules are fixed to the surface of solid substances.

“We fill the containers with an adsorbent, highly porous substance, like activated carbon, made from organic materials. The gas molecules, naturally dispersed, therefore enter the pores in the carbon particles. They group together and reduce the space between themselves”, says José Roberto de Souza, responsible for the Gas Processing Laboratory. It is as if the carbon increased the internal area of the containers, making the molecules find more room for accommodating themselves (see an article on nanotechnology on page 60). This makes it possible to step up the quantity of gas inside the cylinder or other container by as much as 70 times.

The new technology, baptized as ANG, Adsorbed Natural Gas, allows the pressure to fall from 200 to 40 bars. So, when the work is concluded, the tanks will get practically the same 17 cubic meters, without jeopardizing the vehicle’s autonomy. The steel used in the cylinders will make way for carbon fiber, aluminum or other lighter materials. The weight will fall by 30%. The metal tanks may have welding joints impossible in today’s cylinders and will be made in formats that are adapted to the engineering of the vehicle, to favor the distribution of weight.

Compact blocks
“We still need to finds means for improving adsorption and to find out what is the maximum quantity of activated carbon that it is possible to be placed inside the various kinds of tanks. We have also studied structured shapes, compact blocks with larger surfaces where the gas can be lodged, instead of the particles we use today”, Souza says. The ANG technology also may contribute towards a new stage for the use of gas in vehicles, by bringing about an increase in the number of fueling stations. By the figures from BR Distribuidora (The Distribution subsidiary of Petrobras), Brazil had 486 gas stations at the end of last year, almost 70% located in São Paulo, Rio de Janeiro and Minas Gerais. In 11 Brazilian states, there was not even a single station offering natural gas.

There are two reasons for this picture. The first is the prohibitive cost of US$ 250,000 of the powerful compressors available on the market that receive the gas through ducts, at an average pressure of 8 bars, to bring it up to the necessary 200 bars. The fall in the pressure in storage to 40 bars would reduce this cost to US$ 125,000. Companies with fleet of gas-fueled cars call also create small stations for carrying out their own supplying.The other is the still small network of gas pipelines, a little over 5,300 kilometers crossing 14 states. If the gas does not reach the stations through ducts, it has to get there by truck, laden with large, heavy individual cylinders, because of the high storage pressure. A single large tank with a pressure of 40 bars will have a far larger capacity than several cylinders piled on top of each other.

Natural gas is a good alternative energy for cars and factories. Today, this fuel has a 3% share of the national energy matrix. The forecasts are that it will grow to 10% by 2005. Alert to the expansion of this as yet timid market, Petrobras has created the Gas Energy Network, which amongst other projects commissioned the research into the reduction of the pressure of the gas.

Gas for vehicles brings significant advantages. At the same time, it brings relief to the consumer’s pocket, besides being cheaper, it is 20% more economical and pollutes 50% less than gasoline. But the researchers from CTGás will still have to solve another problem that discourages an option for a gas fueled car. Besides the inconvenience of carrying a cylinder in the trunk like an eternal passenger, the cost of conversion is high. Today, it is between R$ 2,000 and R$ 3,000. To bring this amount down, in the next few months they will be beginning a detailed study of the components needed for the equipment, from different manufacturers. The objective is to find good quality parts at lower prices, and so bring down the final cost of conversion.