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We’ve been discussing various aspects of a power plant’s water-to-steam cycle, from machinery specifics to identifying inefficiencies, and today we’ll do more of the same by introducing the condenser hot well and discussing its importance as a key contributor to the conservation of energy, specifically heat energy. Let’s start by returning our attention to the steam inside the condenser vessel. Last week we traced the path of the condenser’s tubes and learned that the cool water contained within them serve to regulate the steam’s temperature surrounding them so that temperatures don’t rise dangerously high. To fully understand the important result of this dynamic we have to revisit the concept of latent heat energy explored in a previous article. More specifically, how this energy factors into the transformation of water into steam and vice versa. Steam entering the condenser from the steam turbine contains latent heat energy that was added earlier in the water/steam cycle by the boiler. This steam enters the condenser just above the boiling point of water, and it will give up all of its latent heat energy due to its attraction to the cool water inside the condenser tubes. This initiates the process of condensation, and water droplets form on the exterior surfaces of the tubes.
The water droplets fall like rain from the tube surfaces into the hot well situated at the bottom of the condenser. This hot well is essentially a large basin that serves as a collection point for the condensed water, otherwise known as condensate. It’s important to collect the condensate in the hot well and not just empty it back into the lake, because condensate is water that has already undergone the process of purification. It’s been made to pass through a water treatment plant prior to being put to use in the boiler, and that purified water took both time and energy to create. The purified condensate also contains a lot of sensible heat energy which was added by the boiler to raise the water temperature to boiling point, as we learned in another previous article. This heat energy was produced by the burning of expensive fuels, such as coal, oil, or natural gas. So it’s clear that the condensate collecting in the hot well has already had a lot of energy put into it, energy we don’t want to lose, and that’s why its an integral part of the water-to-steam setup. It acts as a reservoir, and the drain in its bottom allows the condensate to flow from the condenser, then follow a path to the boiler, where it will be recycled and put to renewed use within the power plant. Next week we’ll follow that path to see how the condensate’s residual heat energy is put to good use. ________________________________________ |
Posts Tagged ‘water droplets’
How A Power Plant Condenser Works, Part 3
Monday, October 14th, 2013
Superheater Construction and Function
Sunday, September 15th, 2013|
Power plants produce electrical energy for consumers to use, whether at home or for business, that’s obvious enough, but did you know that in order to produce that electrical energy they must first be supplied with heat energy? The heat energy that power plants crave comes from a fuel source, such as coal, oil, or natural gas, by way of a burning process. Once the heat energy is released from the coal through burning, it’s transported into a steam turbine by way of superheated steam, which is supplied to it by a piece of equipment named, appropriately enough, a superheater. So what is a superheater and how does it function? Take a look at the illustration below.
The superheater looks like a W. It’s actually a cascading array of bent steam pipe, situated above a source of open flames which are produced by the burning of a fuel source. A photo of an actual superheater is shown below.
So how many bends are in a superheater? Enough to fill the needs of the particular power plant it is supplying energy to. Since all power plants are designed differently, we’ll keep things in general terms. The many bends in the superheater’s pipes form a circuitous path for steam to flow as it follows a path from the boiler to the steam turbine. The superheater’s unique construction gives the steam flowing through it maximum exposure to heat. In other words, the bends increase the time it takes for the steam to flow through the superheater. The more bends that are present, the longer the steam will be exposed to the flame’s heat energy, and the longer that exposure, the more heat energy that is absorbed by the steam. Superheating routinely results in temperatures in excess of 1000°F. This superheated steam is laden with abundant heat energy which will keep the steam turbine spinning and the generator operating. The net result is millions of watts of electrical power. As we learned in a previous blog, the superheater is designed to provide the turbine with sensible heat energy to prevent steam from completely desuperheating, which would result in dangerous condensation inside the turbine. The newly added superheater is a major improvement to a power plant’s water-to-steam cycle, but there’s still plenty of waste and inefficiency in the system, which we’ll discuss next week.
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Condensation Inside the Steam Turbine
Sunday, September 8th, 2013|
Did you know that water droplets traveling at high velocity can take on the force of bullets? It can happen, particularly within steam turbines at a power plant during the process of condensation, where steam transforms back into water. The last couple of weeks in this blog series we’ve been talking about the steam and water cycle within electric utility power plants, how heat energy is added to water during the boiling process, and how turbines run on the sensible heat energy that lies within the superheated steam vapor supplied by boilers and superheaters. We learned that without a superheater there is a very real possibility that the steam’s temperature can fall to mere boiling point. When steam returns to boiling point temperature an undesirable situation is created. The steam begins to condense into water within the turbine. To understand how this happens, let’s return to our graph from last week. It illustrates the situation when there’s no superheater present in the power plant’s steam cycle.
Figure 1
After consuming all the sensible heat energy in phase C in Figure 1, the only heat energy which remains available to the turbine is the latent heat energy in phase B. If you recall from past blog articles, latent heat energy is the energy added to the boiler water to initiate the building of steam. As the turbine consumes this final source of heat energy, the steam begins a process of condensation while it flows through the turbine. You can think of condensing as a process that is opposite to boiling. During condensation, steam changes back into water as latent heat energy is consumed by the turbine. When the condensing process is in progress, the temperature in phase B remains at boiling point, but instead of pure steam flowing through the turbine, the steam will now include water droplets, a dangerous mixture. As steam flows through the progressive chambers of turbine blades, more of its latent heat energy is consumed and increasingly more steam turns back into water as the number of water droplets increases.
Figure 2 – Water Droplets Forming in the Turbine
The danger comes in when you consider that the steam/water droplet mixture is flying through the turbine at hundreds of miles per hour. At these high speeds water droplets take on the force of machine gun bullets. That’s because they act more like a solid than a liquid due to their incompressible state. In other words, under great pressure and at high speed water droplets don’t just harmlessly splash around. They hit hard and cause damage to rapidly spinning turbine blades. Without a working turbine, the generator will grind to a halt. So how do we supply the energy hungry turbine with the energy contained within high temperature superheated steam in sufficient quantities to keep things going? We’ll talk more about the superheater, its function and construction, next week.
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Industrial Ventilation – Local Exhaust Ventilation Filters and Air Cleaners III
Sunday, May 15th, 2011| I was out in the garage today spray painting, a job I would have preferred to have done outdoors, but alas, it was raining. It wasn’t a big job, and I probably didn’t spend more than about an hour doing it, but by the time I was done I was all too aware of how noxious the chemical fumes were that were put out by my aerosol spray can. I had thought that with all the garage doors open and a good cross breeze going through I’d be spared the unpleasant smell. Now imagine this all on a much larger scale, say an industrial setting, where massive spray painters are used all day long.
We’ve been talking for awhile now about filtration, from fabric filters to cyclones, and how they are most effective when integrated into a local exhaust ventilation system. These filtration devices are great for the removal of airborne particles like dust, but they don’t do a good job removing chemical vapors like paint fumes, much in the same way as a dust mask wouldn’t have made my spray painting job any less smelly. This week we’ll focus on filtration capable of addressing the special challenges presented by chemical vapors in the air. Chemical vapor contaminants can be separated from good air trapped in a local exhaust ventilation system by way of an air cleaner in a process known as absorption. In this instance, just like with our smelly goldfish tank, the media can consist of activated carbon, a carbon created by intense heating of substances like bituminous coal, wood, or coconut shell. The heat removes everything except carbon and creates myriads of tiny pores throughout. These pores give activated carbon tremendous surface area, meaning lots of nooks and crannies for chemical molecules to get lodged in. And when I say “lots” of nooks and crannies, I mean it. One pound of granular activated carbon has enough pores to give it a surface area of 125 acres! As the air-vapor mixture passes over the huge surface area, chemical vapors are absorbed by combining chemically with the carbon. Jamb packing surface area into a small space, as activated carbon does, creates a media capable of absorbing vast amounts of chemical molecules for a long time. As effective as this system is, the carbon pores will eventually become saturated with contaminants, and when it does, it is easily addressed. Simply replace the media with fresh carbon. Another means of removing harmful vapors from the air is through the use of an air cleaner employing temperature as its means of filtration. I’ll bet you’re asking how that works, and here’s an example you can relate to. It’s a hot, humid day, and the only thing standing between you and total discomfort is a glass of ice water. As you eagerly lift the glass to your lips, you notice the glass is wet on the outside, so wet that it’s actually dripping. In the stupor caused by your heat exhaustion you may for a moment think that the glass is actually leaking, but you soon realize that the water has accumulated on the outside of the glass because the hot, humid air that is making you so uncomfortable has also come into contact with the cold surface of the glass. When the water vapor in the atmosphere hits the cool of the glass filled with ice, it condenses into droplets. This condensation process stops when the glass temperature equalizes to that of the temperature in the surrounding air. Air cleaners can make use of the same phenomenon to filter contaminants. In their case the contaminated air mixture is cooled to the point where the humidity and chemical vapors present condense together to form a liquid, and the liquid is then drained out for proper disposal. That’s it for our look at filters and air cleaners. To sum things up, remember that there are a variety of factors that have to be considered when selecting filters and air cleaning devices. These include the volume of air flowing through the system, the concentration of contaminants in the air, the chemical and physical properties of the contaminants, the hazards associated with the contaminants, and the emissions standards established by federal, state, and local environmental regulations. Next time we’ll explore the workhorse of a local exhaust ventilation system, its fan. _____________________________________________ |
