Search This Blog

Sunday, April 28, 2013

Stationary Steam Engines

Now this is a subject near and dear to my heart!  Although I love steam trains and marine power plants, you don't get big power without a big engine.

Let's take a concrete example of the power output of mobile vs. stationary engines:  A really powerful modern diesel locomotive can produce 5000 horsepower.  Let's say you are moving a massive train over the mountains and require four big locomotives to move it.  So we need  20,000 horsepower.  Here is an online conversion calculator to watts.  If you don't want to follow the link, the four locomotives, running full blast, produce 14,913,997 watts, or 14.9 Megawatts.

Thats about what a really small gas turbine, hydro, or geothermal power plant makes.

Power stations didn't start out making huge power.  They started out with primitive low-speed engines that  used steam at atmospheric pressure.  These slow-moving engines drove lumber mills, grain mills, textile mills, and low-pressure air blowers for steel foundries.  They were even used for drawbridges.  See photo below.

A huge improvement on the atmospheric condensing steam engine was the Corliss Engine, which was invented in 1849.   There are several issues steam engines have that steam turbines do not have.  One of the big issues is intermittent steam admission into the cylinder.  Therefore valve design and timing are crucial to efficiency.

The Corliss engine greatly increased efficiency by using rotary steam valves (similar to today's ball valves), and introduced variable valve timing for both intake and exhaust.  Below is a cutaway of the cylinder of a Corliss steam engine.  It is a double-acting engine, meaning that steam pushes on the piston from both sides. 

This cutaway shows the inlet steam pipe (1), Rotary Steam Inlet valves (2), Rotary steam exhaust valves (3), Steam exhaust to condenser (4), Connecting rod (5), Piston (6), and Cylinder (7). 

Below is a drawing of a Corliss steam engine.  Steam enters the box containing the cylinder from the pipe at the top right.  The disc at the center of the box is connected by rods to four different rotary steam valves.  The timing of the steam valve opening is mechanically adjusted by the center disk, which in turn rotates back and forth based on the machine speed.  Thus the machine is efficient through a range of speeds.  This was the most efficient steam engine design until the invention of the Uniflow design, followed by the steam turbine.  There are still a few of these in operation today!

Below is a Corliss Engine that was on display in Philadelphia for the US Centennial Celebration.  Here is the Wikipedia entry about it:

The Corliss Centennial Engine was an all-inclusive, specially built rotative beam engine that powered virtually all of the exhibits at the Centennial Exposition in Philadelphia in 1876 through shafts totaling over a mile in length. Switched on by President Ulysses Grant and Emperor Dom Pedro of Brazil, the engine was in public view for the duration of the fair.

The engine was configured as two cylinders side-by-side. Each cylinder was bored to 44 inches (1.1 m) with a stroke of 10 feet (3.0 m), making it the largest engine of the nineteenth century. The Centennial Engine was 45 feet (14 m) tall, had a flywheel 30 feet (9.1 m) in diameter, and produced 1,400 hp.

1 comment:

Anzael LLC said...

Thanks for sharing ..Hope this helps many! VCDB Tool