In EPC project, the activity after engineering is procurement. When we want to procure something, for example water treatment package unit, boiler, fire fighting pump, or else, we usually invite several qualified vendors to bidding and get the price. We usually find the price of several equipments quoted by certain vendors is so high but the technical specification is about the same. I will share my experience about how to evaluate technical specification of Water Treatment Plant package unit and to get cheaper price. I take Water Treatment Plant as a case in this post because I feel I have more knowledge in this area than in other areas.
Evaluating Multimedia Filter Package Unit
Multimedia package unit in Water Treatment Plant is a pretreatment used to remove total suspended solid. It consists of two to three kinds of filter, such as silica sand, activated carbon, and gravel. Some water treatment plant vendor may offer additional carbon filter in separate vessel (so the pretreatment consists of two vessel, multimedia filter vessel and carbon filter). The function of carbon filter mainly is to remove iron and manganese. Iron is a big problem when it clogs reverse osmosis unit so that we need to remove it first.
I list some potential cost reduction in multimedia package unit in water treatment plant. You can discuss with the vendors about this cost reduction possibility without sacrificing the quality and quantity of treated water.
- Makes sure the capacity of multimedia filter and carbon filter is correct. Due to mistakes or something, some vendors may offer larger capacity than what is enough. The lower the capacity, the smaller the tank, the lower the media, and of course the lower the price
- If the vendors offer multimedia filter and carbon filter, you need to negotiate the possibility to reduce the amount of media. For example, if vendor offer two kinds of media in multimedia filter (for example silica sand and activated carbon), you may ask to get silica sand in one multimedia filter and activated carbon in carbon filter.
- Check the thickness of tank painting thickness. If the pressure of the vessel is not so high, you can ask to get thinner painting thickness. It will reduce some cost.
- Check the instrumentation. The most important instrumentation for multimedia filter is pressure indicators. You need to install them to get the indicator when the multimedia filter need to be backwashed. Sometimes, the vendors offer safety valve or air venting. You can discuss the importance of this instrumentation.
- Use existing pump to backwash multimedia filter, don’t buy dedicated one. I reccommend to use existing pump to backwash multimedia filter and not but the dedicated pump to wash multimedia filter
Evaluating Reverse Osmosis Package Unit
Reverse Osmosis water treatment plant is a filtration process use to purify water. It uses to reduce the total dissolve solids and chemical impurities from water. In water treatment plant, reverse osmosis unit is constructed as skid mounted type, consisting of the RO feed pump, cartridge filter, RO high pressure pump, reverse osmosis membrane and pressure vessels, control valves, piping, and all necessary accessories and instrumentation.
| Fluid Phase | Fluid Condition/Description | Tube Side | Shell Side |
|---|---|---|---|
| Liquid | Process Fluid | 1-2 m/s Max 4 m/s | 0.3-1 m/s |
| Water | 1.5-2.5 m/s | 0.3-1 m/s | |
| Vapor | Vacuum | 50-70 m/s | 50-70 m/s |
| Atmospheric | 10-30 m/s | 10-30 m/s | |
| High pressure | 5-10 m/s | 5-10 m/s |
Before we discuss about how to reduce reverse osmosis package unit therefore reduce overall cost to buy water treatment plant package unit, there are several technical aspect you need to make sure when you read the technical specification of reverse osmosis.
- Make sure you give correct water feed specification and correct desired water specification (what is the SDI and TDS of your feed water, what is the desired SDI and TDS?). Membrane element will be selected based on feed water salinity, feed water fouling tendency, required rejection, and energy requirement.
- Make sure vendors simulate reverse osomosis membrane system using appropriate desired water parameter
Click here if you want to read more about designing membrane reverse osmosis in water treatment plant.
This is a short list of potential cost reduction of reverse osmosis water treatment plant.
- Use RO feed pump as cleaning pump. I found some vendors do not offer dedicated cleaning pump in CIP cleaning system. They prefer to use RO feed pump as cleaning pump. I just found a reference that mentioned cleaning pump for CIP should be low pressure pump to minimize production of permeate and to avoid dirt redeposition on membrane element. The material should be SS316 or non metallic composite plastics.
- Take a look at instrumentations. I personally do not reccommend this method. The vendors may offer several instrumentations that seems too many. However, we need to pay attention carefully to their experiences. They usually have several reasonable experiences about the importance of installing the instrumentation. For example, the vendor offer you two units conductivity meter at inlet of reverse osmosis unit and at permeate line. You may think one unit conductivity meter at permeate line is sufficient to determine the quality of treated water is at desired level. In my opinion, you will wonder what the initial water conductivity is and to what extent it’s reduced.
Evaluating Mixed Bed Polisher Package Unit
In water treatment plant, mixed bed polisher is usually installed after reverse osmosis unit when the water quality of less than 1 microohm conductivity is required or higher degree of safety is required to ensure water quality (source). Another source mention that the mixed bed should be about 0.10 microSiemens/cm at 25 degree C and 0.010 to 0.020 mg/L as SiO2 (10 to 20 ppb).
In mixed bed polisher, anion and cation are joined in a single vessel. The two resins are intimately mixed by agitation with compressed air.
I found mixed bed polisher usually contributes the highest price among other water treatment plant package unit because it operates automatically. I have ever asked one vendor about the possibility to change the operation mode of mixed bed polisher from automatic to manual. They said the cost will reduce very significantly.
When you read technical specification of mixed bed polisher for your water treatment plant, you also need to consider the consumption of instrument air because the system uses instrument air during regeneration. You need to check if the consumption is still sufficient with the production of instrument air, unless you need to buy blower.
Although it operates “manually”, you still need alarm if the conductivity increases the level that required regeneration or you need to present the value of flow, conductivity, and pH of treated water in central control room.
Sometimes I found some vendors offer regeneration pump for mixed bed. You may discuss with them about the possibility to use ejector instead of pump so that the cost will reduce.
I hope this summary will help you determine the best price of water treatment plant package units and acceptable water quality. 🙂
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