Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a divisional patent application claiming priority to U.S. patent application Ser. No. 13/758,394, filed Feb. 3, 2013, entitled “Atmospheric Storage Mechanical Weight Batch Blending Plant,” from which U.S. continuation-in-part patent application Ser. No. 14/593,621, filed Jan. 9, 2015 is also pending. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a dry cement batching and blending plant, and more particularly, to a portable dry cement batching and blending plant that will accurately measure and completely blend the ingredients of dry pre-made cement mixtures, which are then mixed with water at the well site for the oil &amp; gas drilling and fracturing industry. 
     BACKGROUND OF THE INVENTION 
     A practice of using cement in the oil industry began around 1903 in California in an attempt to stop water from flowing into the oil well, and oil and gas from entering the waterways (aquifers). In those early years, cement was hand mixed and run into a dump baler to the spot needing to be plugged. Pumping cement, which would be mixed with water, down a well was soon also recognized as beneficial to encase the well and achieve a safer and more efficient operation of the drilling process. A forerunner of the modern two (2)-plug method was first used in 1910. The two (2) plugs minimize mud contact with the cement. Although both mechanical and chemical improvements have been made in a cementing process, the original plug concept is still valid today. 
     Erle Halliburton cemented a well in Oklahoma&#39;s Hewitt Field in 1920. The dry blending of oilfield cements is attained by many means, but the most prevalent remains the pneumatic transfer of the individual constituent parts of cements and additives, which are moved from pressure vessel to pressure vessel. This remains very similar to what was developed in the 1920&#39;s. These moves are often layered or “pancaked” to affect somewhat of a blend when then transferring to the next in a series of tanks. This type of mixing is referred to as “moves”. Moves result in a very unscientific and haphazard blending methodology, as the differing specific gravities and molecular makeup of the varies constituent materials including various cements, bulk powder additives and granulated minerals and chemicals, are not easily comingled. Cement blends produced in this manner are highly dependent on the experience and attention of the blend plant operator. Numerous problems have been encountered with variations in such un-uniform blending which results in the ununiformed blends needing to be “spiked” or modification of the cement blends at the well site prior to mixing with water to get a properly performing and more complete mixture. A poor cement blend mixture can cause many problems including poor set strength, inadequate cement bond, blowouts, poor formation fracing or lack of mud displacement, which in the least presents environmental hazards, and losses in productivity, and in the worst cases can result in severe injury and loss of life due to blowouts and resulting explosions and fire. 
     Because of the inconsistencies in the mix cement product, many oilfield operators have gone to “pod” or “batch mixing”. In the pod or batch mixing, all of the ingredients for the cement are put inside of a mixer and stirred together. This mix of blended cement is taken either in a slurry form or a powder form to the wellhead. At the wellhead, if it&#39;s in the powder form, water is added as the slurry is injected into the well. The using of pod or batch plants solved to some degree the cementing problems at shallow depths. 
     However, over the years, many different types of cements have been developed. The American Petroleum Institute recognizes Class A through Class J of different types of cements. When deciding upon cement job not only does a type of cement have to be selected, but so does the various additives. Many different additives have developed over the years. Oil wells have gotten deeper and deeper, and in recent years drilling is both vertical and horizontal, so the cementing occurs at higher pressures and higher temperatures, and the correct cement blend or mixture becomes more and more critical. Each well service company provides its own particular blend or “recipe” for their cement jobs, especially cement used at depths of 10,000 feet or more and are expected by well owners to provide a high level of quality assurance of high-performing well encasement with the pre-blended cements. The invention allows the utmost in quality assurance to the well service contractor, the well owner, landowner, and the community as a whole, while protecting the well rig workers and the environment. 
     For the blends used at high pressures and temperatures, it becomes important to completely mix (1) large volumes by weight items in the pre-blended dry cements, (2) intermediate volumes by weight of some items in the pre-blended dry cements, and (3) small volumes by weight of additives in the pre-blended cements. All of these must be perfectly pre-blended together to give the ideal cement blend at the well site prior to mixing with water or other fluids. If the ideal dry cement pre-blend is not reached and the cements and additives are not properly applied, blowouts can occur such as the BP Petroleum blowout that occurred in the Gulf of Mexico in 2010. Since the catastrophic BP blowout, more and more attention has been given to the accuracy of the pre-blend of cement being used, especially in deep wells, and in fracturing of wells, and also on offshore drilling. 
     In an attempt to solve the problem of inadequate pre-blending of oilfield cement, many of the larger companies have developed their own system or techniques. For example, Schlumberger Technology Corporation in U.S. Pat. No. 7,464,757, shows a batch mixing facility to deliver homogenized mixing slurry to a well pumping system, but this mixing can only affect the water/fluid-cement ratios and homogenize the mixture with the fluid, and does nothing to affect the imbalance of poorly pre-blended dry cements delivered to the well mixer out of specification of the recipes and safety requirements. 
     One of the problems with the prior systems is when water is added to the cement mixture, the resulting slurry can only be as good as the dry pre-blend, which at present is most unscientific and haphazard resulting in varying quality and unknown performance of the well encasement. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an apparatus to give a measured, dry, and completely pre-blended oilfield cement and additives recipe that can be substantiated in a controlled and measurable fashion as to provide expected performance when mixed with fluids at the well site. 
     It is another object of the present invention to provide a method for weigh-batching and exacting measurement of all constituent materials making up the oilfield cement according to a predetermined formula—by a computerized and controlled method. 
     It is yet another object of the present invention to provide a portable pre-blend dry oilfield cement plant that can accurately blend a dry cement to a measurable quantity by weight according to a predetermined formula. 
     It is yet another object of the present invention to provide a portable blending plant that can blend a dry cement mixture that has (1) bulk ingredients, (2) intermediate ingredients and, (3) small amount ingredients, each being measured by weight, into a complete pre-blend as to allow for multiple small parts to be thoroughly interspersed throughout the mass of the pre-blend. 
     It is yet another object of the present invention to provide a blender that can blend large quantities of dry cement mixtures to provide a completely blended homogeneous dry pre-blended bulk ready-to-mix specialized cement for mixing with fluids at the wellhead. 
     In the blending plant a collection of bulk storage tanks are arranged around a weigh batcher. Mechanical screw augers connect from each of the bulk storage tanks to the weight batcher to provide an automated and recordable dosing of each constituent bulk powder to be blended. The weigh batcher measures by weight a predetermined quantity from selected bulk storage tanks. The measured quantities are then fed to a mechanical blender of a batch-type providing for a consistent and recordable quantity and batch number allowing for traceability and subsequent quality assurance practices so badly required in oilfield well encasement practices to date. 
     Intermediate quantities of ingredients for the cement blend are also weighed and fed into the blender. The intermediate quantities are normally delivered in bulk sacks or bags, rather than in truckloads as for the bulk storage tanks. 
     Also, small amounts of ingredients to be added to a cement mixture are also weighed and delivered to the blender through a drag tube conveyor—nothing is left to hand-add measurements or human error in the invention. The blending plant then automatically and thoroughly mechanically blends under only atmospheric conditions all of the dry ingredient-types (large, intermediate and small in quantities) into a dry homogeneous pre-blend. As soon as the blending is complete, the blender dumps the batch into appropriate weighed and automatically inventoried containers; and starts the blending process begins again in a cycle basis to automatically pre-blend a prescribed total pre-blend quantity of several tons for shipment by bulk transport truck or specialized oilfield bottle truck chassis to the well site. 
     Because the dry cement blend is very abrasive it can damage the bearings on any blender shaft used in a horizontal shaft equipped blender. Also, because any lubricant, such as grease, coming into contact with the cement blend can damage the cement blend, a special bearing was designed that uses pressurized air to (a) keep the cement mixture out of the bearing and (b) provide an air cushion on which the bearing will turn. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustrated perspective view of an atmospheric mechanical weigh batch blend plant. 
         FIG. 2  is a top view of  FIG. 1 . 
         FIG. 3  is a perspective view of the blender used in  FIGS. 1 and 2 . 
         FIG. 4  is an illustrated perspective view of the mini batch portion of the weight batch blend plant shown in  FIGS. 1 and 2 . 
         FIG. 5  is a perspective view of the weigh vessel for measuring intermediate quantities of cementing ingredients of the weight batch blend plant shown in  FIGS. 1 and 2 . 
         FIGS. 6A and 6B  are illustrated flow diagram of the weigh batch blend plant shown in  FIGS. 1 and 2 . 
         FIG. 7  is a cross-sectional view of a bearing used in the blender shown in  FIG. 3 . 
         FIG. 8  is an illustrated flow diagram of the atmospheric storage mechanical weigh batch blend plant. 
         FIGS. 8 a  through 8 i    illustrate electrical controls for the atmospheric storage mechanical weigh batch blend plant of  FIG. 8 . 
         FIG. 9  is a top view of an alternative vertical blender. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIGS. 1 and 2  in combination, an atmospheric storage mechanical weigh batch blend plant, representing by reference numeral  12 , is shown. All of the ingredients of the cement recipe are mechanically forced together inside of the blender  14 . 
     1. Bulk Materials 
     The larger constituent quantities of materials that are needed in a dry pre-blended cement, which are referred to as bulk materials, are stored in atmospheric bulk storage tanks  20 A- 20 F. Bulk materials are received from bulk weigh batcher  16  via dual screw transport augers  18 . Mechanical screw augers  22 A- 22 F feed preselected bulk materials from either bulk storage tanks  20 A- 20 F, respectively, into the bulk weigh batcher  16 . Only preselected amounts of each bulk material from bulk storage tanks  20 A- 20 F is fed into the bulk weigh batcher  16  as is determined by weight. Thereafter, the weighed amount of each bulk material from bulk storage tanks  20 A- 20 F is fed via dual screw auger  18  into the blender  14 . 
     Each of the bulk storage tanks  20 A,  20 C,  20 D and  20 F contain a single bulk material and have dust collectors  24  on the top thereof When the bulk storage tanks  20 A,  20 C,  20 D and  20 F are being filled via vortex elbows  26  and air inside of the bulk storage tank  20  is being displaced, dust collectors  24  prevent dust from being discharged to the atmosphere. 
     Referring to bulk storage tanks  20 B and  20 E, these tanks are split down the middle by dividing wall (not shown) so they can store two different bulk materials. Therefore, two dust collectors  28  and  30  are required as well as two vortex elbows  32  and  34  for split bulk storage tanks  20 B and  20 E. 
     The use of the weigh batcher  16  with the mechanical screw augers  22  where a large amount of the bulk material contained in bulk storage tank  20  may be used, the large amount of material can be accurately weighed and fed through dual screw augers  18  into the blender  14 . 
     2. Intermediate Materials 
     In a typical blend of dry cement that is to be used in deep wells with high pressure and temperatures, there will probably be some intermediate materials by weight in the mix. By intermediate there will not be as much as the bulk materials, but will be more than small amounts. The intermediate materials normally come in bulk bags rather than by the truckloads. The intermediate materials are storage in intermediate storage tank  36  that has a divided wall  38  to divide the intermediate storage tank  36  into two separate halves for two different intermediate materials to be included in the dry mixed cement. Each side of the intermediate storage tank  36  has a bulk bag unloader  40 A and  40 B. The bulk bag unloaders  40 A and  40 B connect to drag tubes  42 A and  42 B, respectively, that delivers the intermediate material to the respective sides of the intermediate storage tank  36  via discharge valves  44 A and  44 B, respectively. 
     When the intermediate storage tank  36  is being filled up, dust collectors  46 A and  46 B insure that no dust is discharged to the atmosphere as air inside of the intermediate storage tank  36  is displaced. 
     If the particular recipe calls for some of the intermediate materials contained in intermediate storage tank  36 , the intermediate materials are discharged to a weigh vessel  48  contained there below (see  FIG. 1 ). The weigh vessel  48  measures by weight an accurate amount of the intermediate material called for from the intermediate storage tank  36 . Once properly weighed, the intermediate materials are moved by mechanical screw auger  50  to the blender  14 . 
     3. Adding Small Amounts to Mixture 
     As wells are getting deeper, temperatures increasing and pressures increasing, a number of additives are combined in the recipe in small amounts. The additives could perform many of the following functions:
         1. Being an accelerator to shorten the setting time;   2. Be a retardant that lengthens the setting time;   3. Increase the density (weight) of the cement blend;   4. Decrease the density of the cement;   5. Change the compressive strength of the cement;   6. Change the flow properties of the cement;   7. Change the dehydration rate of the cement;   8. Extend the cement to decrease the cost of cementing;   9. Be an anti-foam additive to prevent foaming;   10. Include bridging material to plug lost circulation zones.       

     The above listing is just a typical listing of the functions of various additives that maybe included in the cement blend recipe. For the materials that are added in small amounts, also called “additives”, the additives are added in the mini batch facility  52 , which is shown in more detail in  FIG. 4 . The mini batch facility  52 , has a series of weigh vessels  54 A- 54 C in which small amounts of an additive can be accurately weighed and then fed into the drag tubes  28 . 
     Sometimes it is necessary to add an additive by hand, either because it is such a small amount or a decision was made at the last minute to include another additive. In that case, a hand add-on station  58  is provided where the addition can be weighed as added by personnel operating the plant, by hand, on scale  60  and added through the hatch  62 . The small additives are delivered via the drag tubes  56  to the blender  14 . The drag tube  56  moves the small amounts (additives) through a discharge housing  64  where the additives drop through additive tube  66  into the blender  14  (see  FIG. 3 ). 
     By use of these three separate weighing systems, (1) for the bulk materials, (2) intermediate materials, and (3) the small additives, a very accurately measured dry cement material is delivered to the blender  14 . 
     Referring now to  FIG. 3 , a large view of blender  14  is shown. The bulk materials are fed into the blender  14  through the dual screw augers  18 . The intermediate materials are fed into the blender  14  through the mechanical screw augers  50 . The small amounts additives are fed into the blender  14  via the drag tubes  56 , discharge housing  64  and additives tube  66 . A vent  68  that has dust collection therein, allows any air inside of the blender  14  to be displaced as the materials are added. 
     The blender  14  is a dual shaft blender with two shafts  70  extending horizontally through the blender. Specially designed bearings  72  are on each end, as will be discussed subsequently, of the shafts  70 . The shafts  70  are turned by blender motor  74  (see  FIG. 2 ). Extending from the top the blender  14  is ducting  76  that provides displaced atmosphere containing dust to be scavenged in a dust collection device called the blender scavenger—a pollution control device. 
     Referring now to the mini batch facility  52  is shown in  FIG. 4 , enlarged view of the weigh vessel  54  is shown in  FIG. 5 . The weigh vessel  54  is on a stand  78  with the drag tubes  56  (see  FIGS. 1, 2, and 4 ) extending there below. The exact amount of a small additive that is desired is fed into the weigh vessel  54  through opening  80  and then discharged into the drag tubes  56 . The weigh vessel  54  ensures that exactly the right amount of an additive is fed into blender  14  for the correct mixture or “recipe” for the dry pre-blended oilfield cement. 
     Referring to  FIGS. 6A and 6B , a pictorial flow diagram of the various functions on the weigh batch blend plant  12  are shown. The same reference numbers as previously used will be used again, plus new reference numbers for new items. To the far left of  FIG. 6A  is the intermediate storage tank  36  with dust collectors  46 A and  46 B being located there above. The dividing wall  38  separates intermediate storage tank  36  into two halves. Bulk bags un-loaders  40 A and  40 B are used to load the intermediate storage tank  36  with the intermediate materials that are normally delivered in bulk bags. Mechanical screw  50  is used to deliver the intermediate materials to the hopper  82  of the blender  14 . 
     Depending upon the number of intermediate materials that need to be introduced into the blend, a number of intermediate storage tanks can be increased as the desired. A typical number would be two (2) intermediate storage tanks  36  each having two halves, which would then accommodate a total of four different intermediate materials for the concrete blend—although this number may be reduced or added to accordingly as to accommodate blend recipes as required. 
     Weigh vessel  54  is used to put small amounts of additives into the concrete blend. Any number of weigh vessels  54  as is shown in mini batch facility  52  (see  FIG. 4 ) can be added as needed. The additives are fed through drag line  56  into the blender  14 . In a typical example there may be approximately four ( 4 ) weigh vessels  54 . 
     The larger amounts of material that are delivered by truckloads will be stored in bulk storage tanks  20 . Dust collectors  24  keep the discharge of dust from the bulk storage tanks  20  from getting into the atmosphere during loading and unloading. Materials delivered from bulk storage tanks  20  are weighed in a bulk weigh hatcher  16  (see  FIG. 2 ), then delivered via dual screw auger  18  to the hopper  82  of the blender  14 . 
     Inside of the blender  14 , the various ingredients of the dry cement recipe are blended together by dual shafts (not shown in  FIGS. 6A and 6B ) being turned inside of the blender  14  by motors  74 . After the dry cement recipe is completely blended, together with all various additive and constituent materials, it is discharged by gravity from the blender  14  into ready mix hopper  84 . When the product in the post-blend hopper  74  is completely blended (oilfield terminology to describe the mixture before water is added to form slurry is “pre-blend”), the pre-blend as contained in the pre-blend hopper  84  may be delivered to transport vehicle via transport conduit  86  or to pre-blend storage via storage conduit  88 . If the pre-blend is to be stored, the storage conduit  88  connects to fill valves  90  of pre-blend storage tanks  92 . From the pre-blend storage tanks  92  the pre-blend contained therein may be loaded onto transport vehicles at the desired time via control valves  94  and discharge ducts  96 . 
     For almost all recipes of oil field cement blends for a particular formula, when switching to a different formula or recipe, there will be remnants of the prior mixture. To handle these remnants is a reclaimed storage tank  98 . For example, if the blender  14  has remnants of a dry cement pre-blend therein when switching to a different blend, those remnants are pumped via reclaim line  100  to reclaim storage tank  98 . If a transport vehicle has remnants remaining therein, they can also be pumped via reclaim valve  102  to the reclaim storage tank  98 . 
     Likewise, if there are remnants left in pre-blend storage tanks  92  by pressurizing the pre-blend storage tanks  92  with compressor  104 , any remnants remaining therein can be pumped via reclaim line  100  by opening pre-blend reclaim valves  106  via reclaim line  100  into reclaim storage tank  98 . Reclaim dust collector  108  prevents any dust during the reclaim process from being discharged to atmosphere. 
     To get rid of reclaim materials contained in the reclaim storage tank  98 , the compressor  104  pressurizes the reclaim storage tank  98  which then forces the reclaimed material out discharge control  110  for delivery through transport ducts  112  for disposal. If it becomes necessary for the reclaim storage tank  98  to vent to atmosphere, reclaim dust collectors  114  will ensure no dust is discharged to atmosphere. 
     Referring now to  FIG. 7 , the specially designed bearing  72  for the shafts  70  of the blender  14  is explained in further detail. The specially designed bearing consists of an annulus  116  being bolted to the blender housing  118  by bolts  120  pressing plate  122  against the annulus  116 . 
     Through the annulus  116  is a pressurized air fitting that connects via air duct  126  to the shafts  70  to feed pressurized air from the compressor  104  (see  FIG. 6B ) via the air duct  126  to the surface between bearing  128  and shaft  70 . This means there is a cushion of air between bearing  128  and shaft  70 . Also the pressurized air keeps the material being mixed from getting into the area between bearing  128  and shaft  70 . The shaft  70  is literally riding on a cushion of air. 
     Referring to  FIG. 8 , a pictorial flow representation of the atmospheric storage mechanical weigh batch plant  12  as explained in  FIGS. 1 and 2  is shown. Where possible, like numbers as used for  FIGS. 1 and 2  will be used in  FIG. 8 . However,  FIG. 8  will have additional reference numbers and explanations where necessary. The bulk storage tanks  20 A- 20 F feed through conveyors  22 A- 22 F, respectfully, into bulk weigh batcher  16 . Delivery of bulk material from bulk storage tanks  20 A,  20 C,  20 D and  20 E is controlled by butterfly valves  130 . Because bulk storage tanks  20 B and  20 E are split tanks pneumatic actuated butterfly valves  132  are used. The bulk weigh batcher  16  has load cells  134  to accurately measure the amount of bulk material that has been received. Once the proper amount of material has been received into the bulk weigh batcher  16 , it is then delivered via dual augers  18  to the blender  14 . The bulk weigh batcher  16  handles the large quantities of materials that would typically be used in a dry oilfield cement mixture. The quantities being handled by the bulk weigh batcher  16  are larger quantities (percentagewise) of the dry oilfield cement mixture. 
     At the intermediate storage tanks  36 , bulk bags un-loaders  40 A and  40 B receive the bags of material which bags of material are dumped into an intermediate storage tank  36  via drag tubes  42 A and  42 B. 
     Below the intermediate storage tank  36  are pneumatic actuated butterfly valves  136  which controls the amount of intermediate material being delivered to the weigh vessel  48  as determined by load cells  138 . When the proper amount of intermediate material has been received into the weigh vessel  48 , pneumatically actuated butterfly valve  140  is opened and the intermediate material is delivered through mechanical screw auger  50  to the blender  14 . The term “intermediate” refers to amounts by weight that is considerably less than the materials delivered by the bulk weigh batcher  16 , but are much greater than the small additives typically mixed into a dry oilfield cement blend. 
     The mini batch facility  52  as is illustrated in  FIG. 8 , has a series of weigh vessels  54 A- 54 C that can accurately measure small amounts of additives and deliver those small amounts of additives via pneumatically actuated butterfly valves  142  through the drag tube  56 . The drag tube  56  will deliver the small amounts of additives to the blender  14 . 
     Also the mini batch additive weighing portion of the overall facility  52  will have a hand weigh batcher  58  for the hand adding of small amounts of various additives. The hand amounts also feed through one of the pneumatically actuated butterfly valves  142  into drag tube  56 . Each of the weigh vessels  54 A- 54 C has an opening  80  through which the small amounts of additives can be stored. Even the hand weight batcher  58  has a vessel  144  in which to store small amounts of additives. The mini batch facility  52  adds the small portions by weight of materials that are necessary for the dry oilfield cement blend. 
     After the blender  14  has thoroughly forced the dry materials, into a blend, the dry oilfield cement blend is discharged into a post blend hopper holding pre-blended material  84  for either storage or delivery to the well site. Blowers  146  may be used to move the dry pre-blend oilfield cement in hopper  84  typically referred to as “pre-blend”, to either the transport vehicle (not shown) or a storage vessel  148 . The storage vessel  148  could be the same as the pre-blend storage tanks  92  as illustrated in  FIG. 6B . The compressor  104  provides compressed air as needed particularly in operating various pneumatic valves. 
     Turning to  FIGS. 8 a  and 8 b   , the illustrative flow diagram of the atmospheric storage mechanical weigh batch blend plant of  FIG. 8  is given along with the legends for each of the items illustrated being listed in  FIG. 8 c   . In this manner, each of the items shown in  FIGS. 8 a  and 8 b    are controlled as illustrated in  FIG. 8 a    by each of the items as shown in the legend of  FIG. 8 c   . For example, any of the mechanical functions are illustrated by symbols as are contained in the legend of  FIG. 8 c   , such as “load cells”, “pneumatic actuator”, “slide gate”, just to name a few. The illustrative flow diagram as shown in  FIGS. 8 a  and 8 b    is the type an engineer would use.  FIG. 8 c    is the legend that goes with  FIGS. 8 a    and  8   b.    
     Referring to  FIGS. 8 d  through 8 i    in combination, the electrical connections to  FIGS. 8 a  and 8 b    are illustrated. Each of the tanks as illustrated in  FIGS. 8 a  and 8 b    have the same numerical reference in  FIGS. 8 d  and 8 i   . A motor control panel  200  is used to operate all of the controls as illustrated in  FIGS. 8 a  and 8 b   . A description of the item being operated is given in each of the blocks connected to the motor control panel  200 . While a part of the motor control panel  200 , the utility load center  202  controls specific parts of the weigh batch blend plant. 
     Also connected to the motor control panel  200  is additive scale panel  204 , which is used to add the small amounts added to the blend. Use of the term “J-box” as contained in  FIGS. 8 d  and 8 i    is referring to an electrical junction box. 
     The entire operation is run by a programmable logic controller  206  shown in  FIG. 8 f   , which programmable logic controller  206  sets the recipe being used into the weight batch blending plant. Through the use of the programmable logic controller  206 , the recipe can be changed according to the desires of the operator. In one particular oil field, the recipe for the cement may be different than in a different oil field. Therefore, the recipe may have to be changed, depending upon where the end product is being used. 
     Power for the programmable logic controller  206  is provided by computer power unit  208 . It is important that the computer power unit  208  not be subject to power fluctuations and has a backup power source to maintain information in memory. 
     In case any portion of the program needs to be overwritten, an override panel  210  allows the operator to overrun any portion of the plant as is necessary. Through the use of the override panel  210 , if necessary, the entire plant could be run manually. 
       FIGS. 8 a -8 i    illustrate how a typical atmospheric storage mechanical weigh batch blend plant may be controlled. 
     Blower  150  may be used to move any of the dry materials when blending the various ingredients. 
     While the blender  14  as shown in  FIGS. 1, 2 and 3 , is a dual shaft horizontal blender, the blender also could be a vertical shaft blender  152  as illustrated in  FIG. 9 . The vertical shaft blender  152  has a vertical vessel  154  with vertical shafts  156  extending there through. The vertical shafts  156  has paddles (not shown) thereon to blend the material contained within the vertical vessel  154 . The dry materials for the ready mix cement is delivered to the vertical vessel  154  via dual screw auger  18  of the large quantities of materials, mechanical screw auger  50  for the intermediate materials, and drag tubes  56  for the small amounts of additives. All of the materials are fed into the vertical hopper  158  or discharged through lower opening  160  into the vertical vessel  154 . After the appropriate amounts of the various ingredients are discharged through the vertical hopper  158  into the vertical vessel  154  and thoroughly blended therein, the “pre-blend” cement mix is discharged through discharge opening  162  into one of the pre-blend storage tanks  92 . 
     Typically, a vertical shaft blender  152  will be used for smaller batches, but a horizontal shaft blender such as blender  14  is used for larger batches.

Technology Category: c