CO2 block press

Details CO2 block press CO2 block press

2000-09-11

2002-02-26

Doerrler, William (Department: 3744)

Refrigeration

Processes

Fractionally solidifying a constituent and separating the same

Reexamination Certificate

active

06349565

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to the field of dry ice manufacturing, and more particularly to a method and apparatus for producing blocks of dry ice. 2. Description of Related Art
Dry ice is the solid state of carbon dioxide (CO
2
). There are a vast array of applications for dry ice, including the processing and preservation of meats and other foods. Dry ice is the preferred means of cooling in such applications, since it imparts no color, odor, or taste, and has no lingering deleterious effect on the food. Dry ice also is desirable for the processing of food because its sublimes directly from the solid state to the gaseous phase, leaving no residue behind after yielding its cooling effect; therefore, no clean-up or removal of residual liquid is required. Furthermore, CO
2
is neither toxic, poisonous, reactive with other chemicals, nor flammable.
In its solid state, at standard temperature and pressure, carbon dioxide has a constant and stable temperature of −109.33° F. Carbon dioxide is normally transported in its liquid state, and stored in refrigerated vessels at a pressure of about 305 psia, and a corresponding temperature of about 0° F.
Once the liquid CO
2
reaches the manufacturing facility, dry ice is generally formed into one of the two final forms, blocks of dry ice or smaller pellets. Large blocks of dry ice typically are shipped long distances or stored for extended periods, as pellet size pieces sublimate faster.
The basic process for making block dry ice from liquid carbon dioxide has long been known. Dry ice block manufacture has changed little in the last sixty-five years or so. Over this time, various kinds of apparatuses for carrying out this basic process have been devised. Typical of such conventional apparatus is that which is the subject of Great Britain Complete Specification No. 433,018, accepted Aug. 7 1935. Commonly, present ice block manufacturing incorporates the Southwark-Baldwin press. This machine can produce a 220-pound block of ice. This type of dry ice block press utilizes what is conventionally referred to as a liquid injection process.
The liquid injection process injects liquid CO
2
and a binding agent at a pressure above the triple point of CO
2
into the top of a compression chamber. Liquid CO
2
is supplied to the compression chamber from a remotely located CO
2
supply. When the injection process is complete, the liquid CO
2
in the chamber drops below the triple point and undergoes a phase change, thus producing solid CO
2
(snow).
The amount of liquid CO
2
injected into the compression chamber does not produce a complete block of dry ice until the chamber reaches a minimum equilibrium temperature. For example, the minimum equilibrium temperature of TOMCO
2
ice machines is approximately −50° F. This temperature naturally varies between press types. This process of reaching a minimum equilibrium temperature is similar to the cool down period ice machines go through before they start producing blocks that are considered complete.
The liquid CO
2
is permitted to flash through an expansion device and enter the compression chamber over the triple point pressure from a nominal storage pressure, for example, 100 psia, wherein part of the liquid will turn into gas and part of the liquid will solidify. The proportionate amounts of gaseous CO
2
and solid CO
2
depend on the pressure and temperature of the liquid CO
2
fed into the chamber. The lower the pressure and temperature, the greater the proportion of solid CO
2
formed as a result of the free expansion. Liquid CO
2
initially at about 300 psia and approximately −8° F., when allowed to rapidly expand to atmospheric pressure, yields approximately 1.0 pound of dry ice as snow and about 1.5 pounds of vapor.
The gaseous CO
2
is released through an exhaust port typically located near the top of the chamber, and returned to either a recovery unit or the atmosphere. A hydraulic press then compresses the CO
2
snow until a preset hydraulic pressure is obtained.
A timer generally determines the amount of liquid CO
2
injected into the chamber. However, with a timer, there is no compensation for the loss of CO
2
due to the chamber temperature (i.e., the internal heat of steel). Further, this conventional dry ice process does not incorporate controls either to vary the ice block size, or to provide blocks with uniform block density.
Sometimes, blocks of dry ice from a block press are reduced to a smaller size that can more easily be handled and used in many types of applications. Other machines, for example the dry ice pelletizer, produces dry ice pellets. Dry ice pellets are easily packaged by the manufacturer and subdivided by the consumer into convenient portions for use.
Several disadvantages of conventional dry ice manufacturing processes are known, and include: the requirement of mixing a binding agent with the liquid CO
2
prior to injection into the compression chamber; the incomplete and inefficient vapor removal from the compression chamber; the low vapor exhaust rates; the production of blocks having nonuniform densities; and the production limit of single-sized product. Therefore it can be seen that there is a need in the art for an improved dry ice block press that overcomes these and other prior art deficiencies.
BRIEF SUMMARY OF THE INVENTION
Briefly described, in a preferred form, the present invention is a dry ice block manufacturing process including a CO
2
storage vessel to store and deliver the liquid CO
2
, a dry ice production assembly to transform the stored CO
2
into ice blocks, an automated analysis system.
The CO
2
storage vessel incorporates a supply line to supply the dry ice production assembly with liquid CO
2
. A supply flow meter can be located in the flow path of the supply line.
The dry ice production assembly of the present invention comprises a compression chamber, a compressing mechanism and a heating element. Liquid CO
2
flows from the CO
2
storage vessel, through the supply line and flow meter, and then introduced into the compression chamber through one or more injection ports. The liquid CO
2
injected into the chamber then changes into gaseous and solid forms of CO
2
. The compression chamber also has one or more venting ports for the release of built-up pressure, in the form of CO
2
vapor, in the chamber, as the liquid CO
2
proceeds through phase changes.
The compressing mechanism of the dry ice production assembly then compresses the resulting CO
2
snow in the compression chamber into a single mass of solid dry ice. The compressing mechanism includes a piston and piston rod.
Heat is then applied by the heating element of the dry ice production assembly to the chamber walls in proximity to the dry ice block after compression in order to facilitate vapor and product removal from the chamber without dwell time. The introduction of heat also contributes to uniform block density and removes the need to combine the injected CO
2
with a binding agent as is presently done in conventional block manufacturing.
The automated analysis system enables the dry ice production assembly to directly connect to the CO
2
storage vessel, and controls the entire process.
The present dry ice block manufacturing process incorporates numerous novel improvements over conventional press methods. For example, a first advantage of the press of the present invention is a chamber retention assembly of the compression chamber that enables free expansion and contraction of the chamber with temperature changes within the chamber. This freedom of movement prevents damage to the chamber caused by the stresses and strains due to temperature changes.
The chamber can further include filter media placed over one or more of the venting ports in order to maximize the vapor exhaust rate of CO
2
from the chamber. Filters over the venting ports allow such a rapid exhaust rate without traditional concerns including the loss of snow into the exhaust piping. Without the present filters, escaping snow would acc

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