Oxygen Candles and CO2 scrubbers

[Carlobrand]

I should go read Atomic Rockets more often.

http://www.projectrho.com/public_html/rocket/lifesupport.php

"For emergency use, it would be wise to pack away a few Oxygen Candles. These are composed of a compound of sodium chlorate and iron. When ignited, they smolder at about 600°C, producing iron oxide (rust), sodium chloride (salt), and approximately 6.5 man-hours of oxygen per kilogram of candle. Molecular Product's Chlorate Candle 33 masses 12.2 kilos, cylindrical can dimensions of 16 cm diameter x 29 height, burns for 50 minutes, and produces 3400 liters of oxygen."

And that apparently refers to something like this:

http://www.naval-technology.com/contractors/hvac/molecular-products/

http://www.molecularproducts.com/us/products/can33p08a05/can33/details

At that rate, a weeks supply of O2 is available for as little as 28 kilograms. Of course, the thing is wickedly hot, but there ought to be some way to tap that waste heat for energy and give you a bit of electricity as well.

Of course, having oxygen is no help if you don't find a way to deal with the CO2. (This pops up a PDF.)

http://www.google.com/url?sa=t&rct=...=E9JU5lso6_otqq4lPsKQIA&bvm=bv.64125504,d.aWc

Two 11 kg boxes provide enough filtering to keep a 1000 cubic foot (28.3 kiloliters, about 2.1 dTons) room with 10 people at safe levels for 3 hours.

Thinking in terms of a cutter with a 30 dT/60 person passenger module, forced to serve as a life boat:

We'd need 672 CASPA boxes to last out a week, a bit under 11 cubic meters in storage. We'd need around 1600 kilograms of oxygen candles if that 6.5 hour per kilo bit is accurate, which is about as 1.6 cubic meters. Less than a dTon serves the craft for a week. Given that we find survival kits with survival rifles and shelter suits in the Marooned lifeboat, and that most of a system is within a few days thrust of a typical rescue craft, provisions for emergency life support for one person for a week could handily be part of the standard equipment for that half-dTon space allocated to the passenger couch - needs only 0.4 cubic meters of the 6.25 available. It's uncomfortable, but it's survivable.

 

[Drakon]

O2 candles

In the 1980's I rode submarines. While my first boat had an O2 Generator, my second boat used O2 candles. 1 candle about the size of a number 10 can, (A big, cafateria or restarant sized can, about 2 or 3 liters in size), would provide enough O2 for a 120~150 man crew 1 hours' worth of O2. Weight I don't recall, maybe 10 kilos?

Reading your description gives me flashbacks.

It does get quite hot, and you could use, if nothing else, thermocouples to generate power. There are really many ways of doing this at TL 7.5. Later tech levels will be more efficient.

The big problem with CO2 removal is what do you do with it? Mechanical scrubbers will recycle the scrubbing fluid, and the CO2 was pumped overboard. In space, that would not always be advisable because of Newton. Chemical scrubbers, like lithium hydroxide, locks up the CO2 where it is.

 

[rancke]

How about an ultra-tech version that consumes CO₂ (locking it up in some innocuous substance) and produces less heat (using a different chemical reaction)?


Hans

 

[Drakon]

How about an ultra-tech version that consumes CO₂ (locking it up in some innocuous substance) and produces less heat (using a different chemical reaction)?


Hans

Like Lithium hydroxide? It is a white powder. That will work. As an emergency, you can take it and spread it on the deck to pull CO2 out. We never had to do that.

The downside is after a while you saturate the lithium hydroxide.

 

[rancke]

Like Lithium hydroxide? It is a white powder. That will work. As an emergency, you can take it and spread it on the deck to pull CO2 out. We never had to do that.

The downside is after a while you saturate the lithium hydroxide.

If it's a part of an ultra-tech oxygen candle it would presumably be calibrated to remove an amount of CO₂ equivalent to the amount of oxygen released. It might not be an actual candle but a box with a button you press. The CO₂ would be locked up inside the box, ready for eventual disposal. Or perhaps the CO₂ is turned into carbon and O₂ -- some sort of artificial photosynthesis perhaps.


Hans

 

[Lycanorukke]

Instead of going the raw chemical candle route with U-tech, use a bioreactor. A self contained unit which contains geneered bacteria which draw their energy from electricty (as opposed to photons) and nutrients.

When you what to switch it on - plug an activation tube (containing a battery, nutrients, water and 'seeding' bacteria) into the box and the bacteria get to work eating the Co2, spiting out oxygen and making more bacteria. Once the tube 'runs out', plug in another one.

 

[atpollard]

The big problem with CO2 removal is what do you do with it? Mechanical scrubbers will recycle the scrubbing fluid, and the CO2 was pumped overboard. In space, that would not always be advisable because of Newton. Chemical scrubbers, like lithium hydroxide, locks up the CO2 where it is.

Since the ship has no problems storing Hydrogen as a liquid, it should be simple to store surplus CO2 as a solid - a can of dry ice to keep your beer cold.

 

[Carlobrand]

Since the ship has no problems storing Hydrogen as a liquid, it should be simple to store surplus CO2 as a solid - a can of dry ice to keep your beer cold.

I'm assuming this is an emergency situation, or else you're using these as part of a small craft cabin - which is to say relying on inexpensive alternatives so you don't have to spend half a million for the good tech. In either case, you're not spending extra on measures to clean and store the CO2, you're relying on inexpensive solutions that will serve the need for whatever period you expect the need to be served - after which you're basically in the same situation as the miners trapped below for too long.

 

[esampson]

Assuming a reasonably high technology (above 8 but probably well below 15) I would envision the following as an 'emergency candle':

When packaged the emergency oxygen supply resembles nothing more than a very large can covered in a wrapper. When unwrapped both ends are show to be 'pop top' designs with holes placed around the walls of one end. With the top and bottom pulled off the contents of the can are a fairly large volume of water, a packet of 'burs' about the size of marbles, a solid divider which separates the inside of the empty can into two open compartments, and a small sealed chemical pouch similar to an emergency cold compress (stored in the side of the can with the holes).

The can is stood up with the end of the can with the holes on the ground, deck, etc. Water is poured into the top compartment of the can and the 'burrs' are added. The sealed chemical pouch is 'smacked' to break the internal pouch and the entire can assembly is placed over the pouch.

Heat generated by the chemical pouch fuels catalytic reactions within the 'burs' to absorb CO₂ out of the air and bond it with the hydrogen in the water forming simple hydrocarbons (starches and sugars) and releasing the oxygen contained within the water. This is basically the same process as photosynthesis but at an accelerated rate. The reason for the bur shape is to maximize surface area and the individual burs are fractal shapes similar to

.

The can can be emptied as needed and if reasonably clean water can be added the reaction can continue for a very long period of time as long as a strong heat source is present. The heat source would need to be anaerobic so a simple fire probably wouldn't work (a chemical fire could be used as long as it was generating sufficiently high levels of heat while consuming fairly low amounts of oxygen but simply burning wood or equivalent material probably wouldn't work).

There would be variations on the basic design. Some variations might replace the chemical pouch with multiple smaller pouches to give more control over the production of oxygen (since you couldn't stop the reaction once it began). Some variations could include a setup with some nesting cups and a filter so that impure water sources could be filtered while the initial water supply is being used (less pure water will cause a buildup of byproducts that are not part of the reaction which can clog or otherwise impede the catalysts). The core design concept would remain the same, however.

 

[aramis]

A genuine Oxygen candle system (9.2x9.2x25.5cm, roughly 1.8L, 0.85kg) generates 36 L of medical grade oxygen as a byproduct. It's an exothermic reaction of sodium chlorate and iron, and produces surplus oxygen. Light it, and it burns, ~600°C, releasing more oxygen. than anything else. The unit mentioned above generates 2.5L-3L for 12-15 minutes, and includes the needed thermal protections for use in confined spaces.

Larger ones in the 25L range can generate 30kL of O2.

Note that a human uses around 500-600 L per day. Less when inactive, more when active. So the human need is roughly 23L and hour. Just to give you an idea - that Oxygen Candle above, burning 15 minutes, releases 1.5 man-hours of oxygen. (I find a nominal resting awake rate of 3.5 mL/(kg•min) . Peak use is 30-40 mL/(kg•min).)

http://www.trifoot.ch/english/oxygen_candle.html
http://www.pharmaceutical-int.com/article/oxygen-generation.html

 

[Carlobrand]

A genuine Oxygen candle system (9.2x9.2x25.5cm, roughly 1.8L, 0.85kg) generates 36 L of medical grade oxygen as a byproduct. It's an exothermic reaction of sodium chlorate and iron, and produces surplus oxygen. Light it, and it burns, ~600°C, releasing more oxygen. than anything else. The unit mentioned above generates 2.5L-3L for 12-15 minutes, and includes the needed thermal protections for use in confined spaces.

Larger ones in the 25L range can generate 30kL of O2.

Note that a human uses around 500-600 L per day. Less when inactive, more when active. So the human need is roughly 23L and hour. Just to give you an idea - that Oxygen Candle above, burning 15 minutes, releases 1.5 man-hours of oxygen. (I find a nominal resting awake rate of 3.5 mL/(kg•min) . Peak use is 30-40 mL/(kg•min).)

http://www.trifoot.ch/english/oxygen_candle.html
http://www.pharmaceutical-int.com/article/oxygen-generation.html

The CAN-33 that I mention is a larger device - 7.4 liters volume - and the manufacturer claims 440 liters of oxygen per liter volume, or 3341 liters for the unit. It's intended as an emergency device for submarines and "underground safe havens". Your 25L units would appear to achieve up to 1200 liters per liter volume of device. I presume the difference relates to the ability to scale up, needing less volume for thermal protection. I wonder what the mass of actual chemical is in these various devices.

 

[aramis]

The CAN-33 that I mention is a larger device - 7.4 liters volume - and the manufacturer claims 440 liters of oxygen per liter volume, or 3341 liters for the unit. It's intended as an emergency device for submarines and "underground safe havens". Your 25L units would appear to achieve up to 1200 liters per liter volume of device. I presume the difference relates to the ability to scale up, needing less volume for thermal protection. I wonder what the mass of actual chemical is in these various devices.

Find a third data point and we can estimate the scaling factor...