Modeling a Portland Cement Plant

The genesis for this project was the re-release of the Walthers HO-Scale "Valley Cement" structure kit. I purchased two kits with plans of "kit bashing" them into a larger plant that will be located at the end of a freelanced Western Pacific branch line in northern California. I envision inbound WP GS Gondolas loaded with limestone, along with other raw materials, being transformed into Portland Cement that will then be hauled away from the plant in short PS-2 covered cement hoppers and 50' boxcars. A little research, on the internet, revealed some significant shortcomings in my original planning.

History & Manufacture of Portland Cement

A British stone mason by the name of Joseph Aspdin invented and received a patent for Portland Cement in 1824. His original batch of cement was produced by heating a mixture of finely ground limestone and clay in his kitchen and then grinding the mixture into a powder creating a hydraulic cement that hardens with the addition of water.

The four essential elements for making contemporary Portland Cement are calcium, silicon, aluminum and iron. Limestone, is the major ingredient for making Portland Cement and the initial process involves combining the limestone with clay and crushing it. Sand, iron ore and bottom ash are then added in the right proportions and the mixture is ground into powder.

Two different methods, dry and wet, are used to manufacture Portland Cement. In the dry process, raw materials are proportioned, ground to a powder, blended and fed to the kiln dry. In the wet processed a slurry is formed by adding water prior to the grinding and blending process. About 70% of US producers use the dry process.

After blending, the mixture of raw materials is fed into the upper end of a tilted rotating cylindrical kiln. The mixture passes through the kiln at a rate controlled by the slope and rotational speed of the kiln. At 2700 degrees a series of chemical changes take place the cause the raw materials to fuse and create "clinkers" about the size of marbles. As the clinkers exit the kiln, they are cooled, combined with gypsum and ground into a fine gray powder - Portland Cement. The rotary kiln is fired by powdered coal, fuel oil or natural gas.

Dry Process Diagram

Modeling a Dry Process Cement Plant

The Walther's kit consists of five major components; a concrete reinforced raw material building, a kiln building, a rotating drum (rotary kiln), a finishing mill building and cement storage silos. Initial construction started with the cement storage since I new exactly what I wanted to do with them. I combined both kits for a total of 16 silos with a covered loading tunnel on each side for loading bulk cement into covered hoppers. Construction is straight forward with the exception of the joints. Even with lots of effort and careful alignment when gluing, the joints have to be filled with putty and sanded smooth before painting. The combined silos are about 18" long, 10" wide and 12" tall. When the basic assembly was finished, I placed the silos on the layout in their proposed location. Painting, details and weathering will wait until all the structures that make up the complex are completed. Waiting allows me the freedom to move things around without worrying about damaging paint or details. It also makes it easier to make modifications which I have a habit of doing. In hindsight, I wish I had added another 8 silos.

Next on the agenda were what Walthers describes as "bulk storage buildings". I believe they are better described as pre-blend raw material storage buildings. Pre-blend is a combination of limestone and clay that has been through the initial crushing process. A overhead longitudinal conveyor will bring the raw material into the buildings from storage silos and a underground feed and conveyor system will move the pre-blend out of the structure and through the grinding and additive process. Most modern Portland Cement plants store pre-blend under domes or outdoors.

Walthers describes this as the "kiln" building. It houses the blender and roller mill. I combined the structures from both kits, as can be seen by the joint down the middle of the building, and built the addition on top of roof from left over parts. This building is about 12" long, 5" wide and 9" tall not including the additive silos. The white additive silos came from a Walthers "Magic Pan Bakeries" kit. I left off some of the piping (for liquids) but they are mostly built per the instructions.

A more modern dry process plant would have a pre-heater tower about 150' tall. Using exhaust gases, ducted from the rotary kiln, to pre-heat the raw materials before they enter the rotary kiln makes the plant much more energy efficient.

Each of the Walthers Valley Cement kits include a rotary kiln that is about 12" long. The shortness of this kiln, less than 100 scale feet, was the primary motivation for purchasing two kits. Even when two kits are combined the resulting rotary is much shorter than all but the most modern dry process plants with pre-heater towers. A more typical rotary kiln would be 3-400' long. Lots of cutting, filling and sanding were required to make the rotary kiln presentable. Walthers makes a motorizing kit that can be added to make the kiln actually rotate. When the rotary kiln was finished, I came to the realization that I was running out of room fast andI would need more than the original 8' feet I had planned on.

The last major structure included with Valley Cement is the finishing mill. It houses the cooling grates, heat exchanger, clinker silos, flyash, limestone and gypsum silos (additives) and the cement grinding mill. Once the processing is complete, the finished Portland Cement is elevated and transferred to the storage silos for loading in trucks or railcars.

A Walthers Glacier Gravel was kit bashed and incorporated into the finishing mill to blend, store and load additional grades of Portland Cement. The two smaller storage buildings in the foreground are from the Walthers Clayton County Lumber kit.

These two photos show most of the major components of the Cement Plant in close to their final positions. Most of the structures will be located on a removable section of 2" pink foam. The sub-roadbed is 3/4" plywood.

The large raw material storage bins built from the Walthers Western Coal Flood Loader kits will be just to the rear of the unloading shed (blue green structure built from Pikestuff engine house

The complex has grown considerably. The original plan called for 2X8 foot complex to be at the end of a branch line in one corner of my train room. It is now positioned along a 26' wall on the other side of the room with the main line dropping down a 2% grade in front of the complex. The mill complex is now about 13 feet long and up to 3 feet wide a one point.