Lime_Slaker_Pre-Design_Report_-_FINAL_09-06-2024_(002).pdf

Lompoc Water Treatment Facility Lime Slaker Replacement Pre- Design Report - FINAL

September 5, 2024

Prepared for:

City of Lompoc, CA

Prepared by:

Stantec Consulting Services Inc.

200 East Carrillo Street, Suite 101 Santa Barbara CA 93101-2137

184031635

Revision Description Author Quality Check Independent Review V1 Draft Z. Movassaghi /

A. Devries 4/29/24 D. Pernitsky 5/2/24 C. Bromley 4/30/24

V2 Final Z. Movassaghi / A. Devries

9/5/24 D. Pernitsky 9/5/24 C. Poytress 9/5/24

LOMPOC WTP LIME SLAKER REPLACEMENT PRE-DESIGN REPORT

Sign-off Sheet iii

This document entitled Lompoc Water Treatment Facility Lime Slaker Preplacement Pre- Design Report was prepared by Stantec Consulting Services Inc. (“Stantec”) for the account of City of Lompoc (the “Client”). Any reliance on this document by any third party is strictly prohibited. The material in it reflects Stantec’s professional judgment in light of the scope, schedule and other limitations stated in the document and in the contract between Stantec and the Client. The opinions in the document are based on conditions and information existing at the time the document was published and do not take into account any subsequent changes. In preparing the document, Stantec did not verify information supplied to it by others. Any use which a third party makes of this document is the responsibility of such third party. Such third party agrees that Stantec shall not be responsible for costs or damages of any kind, if any, suffered by it or any other third party as a result of decisions made or actions taken based on this document.

Prepared by (signature)

David Pernitsky

Reviewed by (signature)

Charles Bromley

Approved by (signature)

Carrie Poytress iv

Table of Contents

1.0 INTRODUCTION

2.0 DESIGN CRITERIA

3.0 EVALUATION OF LIME SLAKING TECHNOLOGY

3.1 SLAKER TYPES

3.2 SLAKER EQUIPMENT PROVIDERS

3.2.1 Option 1: Chemco Detention Slaker

3.2.2 Option 2: Chemco Batch Slaker

3.2.3 Option 3: RDP Batch Slaker

3.2.4 Comparison of Slaker Technologies

3.3 SLAKER EQUIPMENT PROCUREMENT

4.0 BASIS OF DESIGN

4.1 PROCESS MECHANICAL

4.2 STRUCTURAL

4.3 ELECTRICAL AND INSTRUMENTATION AND CONTROLS

4.4 CONSTRUCTION COORDINATION AND CONSTRAINTS

5.0 NEXT STEPS – DETAILED DESIGN

LIST OF TABLES

Table 1: Lime Slaking Equipment Design Criteria Table 2: Comparison of Lime Slaker Systems Table 3: Major Equipment Materials of Construction Table 4: Electrical Load List Table 5: Detailed Design Drawing List Table 6: Detailed Design Technical Specification List

LIST OF FIGURES

Figure 1: Process Flow Diagram for Lompoc WTP Figure 2: Example of a Detention Slaker (Chemco) Figure 3: Example of a Batch Slaker (RDP) Figure 4: Chemco Rotary Feeder Figure 5: Chemco Detention Slaker Mixing Tank Figure 6: Chemco Detention Slaker Degritter Figure 7: Chemco Detention Slaker Before and After a Manual Clean Figure 8: RDP Load Cells Figure 9: RDP Dosing Assembly Figure 10: RDP Degritter Figure 11: RDP Batch Slaker Mixing Tank Before and After Automated Cleaning Cycle Figure 12: Preliminary Equipment Layout at First Floor Figure 13: Preliminary Equipment Layout at Basement Figure 14: Proposed Strengthening for New Equipment v

Figure 15: Photo of the Existing MCC B Motor Control Center

LIST OF APPENDICES

APPENDIX A BUDGET EQUIPMENT QUOTES

APPENDIX B TECHNICAL SPECIFICATION FOR LIME SLAKER EQUIPMENT

1.0 INTRODUCTION

Stantec is pleased to present this Pre-Design Report to the City of Lompoc (City or Lompoc) which summarizes our recommendations for replacement of the existing lime slaking equipment.

The City of Lompoc’s potable water system relies on the existing lime softening system to remove iron, manganese, and hardness. The existing lime slaking and lime feed equipment has reached the end of its useful life and has several ongoing operations and maintenance issues. For these reasons, the City wishes to proceed with the pre-design engineering and the preparation of a procurement package to replace the existing lime slaker equipment with two new slakers and associated equipment, each with a design capacity of 10 MGD. An overview of the overall WTP process is shown in Figure 1.

Figure 1: Process Flow Diagram for Lompoc WTP

The existing lime storage and feed system consists of a pneumatic lime unloading station, two active lime silos, two 1200 lb/hr detention-style slakers, and lime slurry pumps which add lime to the sludge return lines to the clarifiers. This equipment is nearing the end of its useful life and is requiring increasing operations and maintenance time to keep running.

The following system components will be replaced or updated as part of this project:

• Silo fill system piping reinforcement

• Silo ventilation and dust filter systems

• Storage silo knife gates

• Slakers

• Grit removal equipment and bins

• Slurry storage tanks and feed equipment

• Additional breaker in MCC-B

Details of the proposed upgrades are described in the following sections.

2.0 DESIGN CRITERIA

Design Flow: The new lime slaking equipment will be sized for the plant’s overall permitted flow of 10 MGD. The 2021 annual average flow rate and the peak day flow rate were 3.6 MGD and 5.7 MGD, respectively. It is expected that the annual average flow rate will reach 5.2 MGD in year 2045, while the peak day flow rate in year 2045 will be 8.2 MGD. The current permit flow for the Lompoc WTP is 10 MGD.

For the purposes of this assessment, an ultimate design capacity of 10 MGD was used for sizing the slakers.

Lime Dose: The lime dose used in the plant was estimated from 2021 CaO consumption in which 3.8 million lbs of dry quick lime was used, corresponding to an average daily usage of 10,000 lb/day and an average lime dose of 327 mg/L as CaO. In 2024, Operations staff data confirmed that daily lime doses continued to be in this range, with peak usage of up to 15,000 lb/d reported for high-flow days. To account for daily variations in lime use, we have assumed that applied lime doses will vary between 300 and 400 mg/L as CaO. Table 1 shows the associated lime usage for the design flow rates listed above.

Lime Storage: The plant currently uses two of the four existing silos for lime storage. Based on the as-built drawings, each silo has a volume of approximately 2000 ft3, which corresponds to a weight capacity of 110,000 lb. One silo is operated until it is down to 30,000 to 50,000 lbs, then it is taken offline and refilled while the other silo is used. A design guideline of providing 14 days storage at average lime dose and average flow was assumed for this project. As shown in Table 1, the two existing lime silos can provide 14 days of storage under average dose / average flow conditions up to 2045. If additional storage volume was desired, it could be possible to re-instate the two currently unused soda ash silos. The existing silos have bin activators and these existing bin activators will be reused.

Slakers: As shown in Table 1, a slaker capacity of 1463 lb/hr would meet the max dose and max permitted flow (10 mgd) condition. Approximately 300 lb/hr would be adequate to meet the low dose condition at a low flow of 2.7 mgd (data not shown in Table 1). To accommodate this operating range, slaker throughput (for detention slakers), batch time (for batch slakers) and the slurry strength (as %weight solids) can be adjusted. One duty slaker sized for the full design capacity and one identical standby slaker will be provided. We have evaluated manufacturer’s standard-size slakers that can provide up to 1000 lb/hr when producing a 10% slurry and up to 2000 lb/hr at a 20% slurry. As shown in Table 1, the duty slaker would operate with a 10% slurry until the lime demand exceeded 1000 lb/hr, at which point the %solids in the slurry would be increased. A maximum of 14% solids would be required to meet the 10 mgd permitted capacity at the maximum design lime dose.

Each slaker will be equipped with a dedicated lime slurry aging tank and a dedicated grit removal system.

Slurry will be fed to the sludge return line in the Chemical Building basement, as is currently done.

Design criteria for sizing replacement lime slaking equipment are summarized in Table 1.

Table 1: Lime Slaking Equipment Design Criteria

Design Scenario 2021 Low 2021 Avg 2045 Avg 2021 Peak 2045 Peak Max Permit Flow (MGD) 2.7 3.6 4.7 5.7 8.2 10 Chemical Data Quick Lime Quick Lime Quick Lime Quick Lime Quick Lime Quick Lime

Lime Purity 95.0% 95.0% 95.0% 95.0% 95.0% 95% Bulk density (lb/ft3) 55 55 55 55 55 55

Lime dose (mg/L as CaCO3) Minimum 536 536 536 536 536 536

Average 584 584 584 584 584 584 Maximum 714 714 714 714 714 714

Lime dose (mg/L as CaO) Minimum 300 300 300 300 300 300

Average 327 327 327 327 327 327 Maximum 400 400 400 400 400 400

Chemical Usage CaO (lb/day) Minimum 7111 9481 12378 15012 21596 26337

Average 7751 10335 13492 16363 23540 28707 Maximum 9481 12642 16504 20016 28795 35116

Storage Silos Number of storage days required 14 14 13 14 14 14

Required Storage (tons) (14 days at avg dose) 54 72 88 115 165 201 Rated Capacity per silo (tons) 55 55 54 55 55 55

Number of Silos Required 1.0 1.3 1.6 2.1 3.0 3.7 Slaking System Capacity (lbs/hr)

Minimum 296 395 516 626 900 1097 Average 323 431 562 682 981 1196

Maximum 395 527 688 834 1200 1463 Lime Slurry Concentration, by wt., after dilution 10% 10% 10% 10% 12% 14%

Specific Gravity, after dilution 1.07 1.07 1.07 1.07 1.08 1.09 Density of slurry (lbs/gallon) 8.93 8.93 8.93 8.93 9.01 9.10

Aging/Slurry Tank Retention time (hrs) 1.0 1.0 1.0 1.0 1.0 1.0

Total storage required, gallons 365 487 635 771 932 982 Slurry Pumps (gpm)

Minimum 5.5 7.4 9.6 11.7 13.9 14 Average 6.0 8.0 10.5 12.7 15.1 16

Maximum 7 10 13 16 18 19

3.0 EVALUATION OF LIME SLAKING TECHNOLOGY

3.1 SLAKER TYPES

The lime slaking reaction reacts quicklime (CaO) with water to produce a slurry containing reactive Ca(OH)2 particles. Reactivity is a function of particle surface area, which is influenced by slaking temperature, water chemistry, mixing intensity and detention time in the slaker, and the quality of the raw quicklime used. Slaking temperature is generally controlled in the range of 185-195oF, with higher temperatures resulting in a more reactive slurry but also can lead to hot spots in the slurry mixture and reduce hydrated lime effectiveness, Greater slurry viscosity can also occur at temperatures above 180oF.

Slaking temperatures from 175 to 185 oF are more practical.

A minimum reaction time of 3 minutes is typically required for a high-quality raw quicklime, but in some cases up to 20 minutes may be required to completely react a lower-quality lime. If insufficient reaction time is not provided, product is wasted as grit and slaking reactions can continue outside of the slaker, which can result in safety issues (due to the continual evolution of heat) and equipment scaling and fouling.

Several different types of lime slakers are commonly used in municipal lime slaking applications: paste slakers, detention slakers, and batch slakers. Paste slakers are significantly different in operation to detention and batch slakers, so to maintain consistency with the operation of the current detention-style slakers, only detention and batch slakers were considered for the new equipment. Detention and batch slakers are described in general, below. Specific details and features of equipment from various vendors will be discussed in Section 3.2

Detention Slakers: Detention slakers are relatively simple pieces of equipment (Figure 2). In a detention slaker, lime and water are continuously added to a mixing tank where the vigorous mixing produces a slurry. In a modern detention slaker, lime is fed at a water to lime ratio of approximately 4:1 and then the lime or water feed is adjusted to maintain proper slaking temperature; more water to decrease the temperature and more lime to increase the temperature. A detention time of 6-12 minutes is typically provided. Because the mix tank is a fixed size, detention time is reduced as throughput is increased. A portion of the flow continuously exits the slaker mixing chamber and overflows to the integral grit remover where heavier material settles to the bottom of the tank and is subsequently removed as waste by a screw. The de-gritted slurry is then sent to a slurry aging tank (also termed a slurry storage tank) and then pumped to the process feed points. Detention slakers are generally operated at 10-15% slurry concentration when furnished with screw grit removal, although operation at up to 20% is possible with some equipment.

Figure 2: Example of a Detention Slaker (Chemco)

Operationally, detention slakers work best when there is a consistent raw lime product quality and consistent operating conditions. If a batch of lower quality lime is received, the operator may not be able to reduce the throughput sufficiently to completely react the lime.

Batch Slakers: Batch slakers (Figure 3) offer additional process control compared to detention slakers and are generally good for low lime consumption applications. With a batch slaker, a predetermined volume of water is added to the reactor, which is essentially a mixing tank. Lime is then measured out, either by volume or weight, and added to the water. This method allows for precise control of the lime:water ratio and the slurry concentration. The reactor is then mixed and the slaking temperature is monitored. As the slaking reaction proceeds, the temperature increases. When slaking is complete, the temperature reaches a steady state. At this point, the contents of the reactor are transferred to an aging tank where the slurry is degritted and then pumped to the process application points.

Because the slaker operates in a batch mode, the reaction time can be extended to allow completion of the slaking reactions in the case of a low-reactivity lime batch, thereby significantly reducing grit formation, waste, and scaling of downstream equipment. However, because operation is intermittent, batch slakers are larger than detention slakers of an equivalent capacity. Batch slakers generally offer lower maintenance requirements and minimal parts replacement when compared to detention slakers.

Figure 3: Example of a Batch Slaker (RDP)

3.2 SLAKER EQUIPMENT PROVIDERS

Two equipment manufacturers were contacted to provide detailed technical submissions and budget quotes for new lime softening equipment for Lompoc: Chemco and RDP Technologies. These manufacturers were selected based on their suitability for installation in the Lompoc WTP, the quality of the lime slurry produced, equipment quality and reliability, and the favorable reviews they have received by operations and maintenance staff at other installations. Three options were evaluated:

1. Chemco Detention Slaker

2. Chemco Batch Slaker

3. RDP Batch Slaker

3.2.1 Option 1: Chemco Detention Slaker

Chemco can supply either a detention or a batch slaker. The detention slaker is smaller and lighter. The scope of supply for the Chemco system consists of the following major components:

• Two new silo discharge transitions and knife gates

• Two 1500 lb/hr volumetric rotary feeders

• Two detention slakers 1500 lb/hr at 10% slurry concentration

• Two 1300-gallon lime slurry storage tanks

• Two lime slurry feed pumps (peristaltic hose pumps)

• Two lime system control panels

Chemco proposes to remove the existing day hoppers and install a new metal transition and a new knife gate and directly feed lime from the existing silo to the volumetric feeder. A volumetric rotary feeder is used to meter dry lime into the slaker (Figure 4). The rotary feeder is calibrated in the factory to deliver a certain volume of dry lime for each revolution of the feeder. This approach has moderate accuracy but is simple and inexpensive. The feeder has flexible, adjustable vanes (paddles) that allow the feeder to continue working in the presence of larger grit particles in the lime from the silo. These vanes can be adjusted as they wear.

Chemco uses a dust and vapor management system to pull steam and dust out of the slaker headspace so that it does not cause fouling of the screw feeder. This vapor control system will result in much less fouling than is experienced with the current equipment. The slaking process operates up to 190oF, so it creates steam and humidity in the slaking chamber. The dust and vapor management system is designed to scrub the dust and prevent the hot, humid air from rising back into the feeder. If the air rises up into the feeder (of any type of slaker), the humidity in the air will pre-slake the CaO and cause clumping/clogging in the feeder. This leads to various feed issues. Each slaker will have a dust and vapor management system, which includes a stainless-steel canister with stainless steel spray nozzles and a draft inducing fan. This system is running when the slaker is ON and has an interlock to keep it running for a minimum of 6 hours after the slaker is turned OFF to prevent any residual humidity from rising into the feeder. The draft fan pulls the air across multiple spray nozzles that capture the dust. The water and dust are then recycled back into the grit process to not waste water. To avoid pulling a vacuum on the slaker, there is a clean air inlet strategically located on the discharge of the feeder. This way, the airflow is drawn through the feed chute, away from the feeder, to push the air away from the feeder.

Figure 4: Chemco Rotary Feeder

As was shown previously in Figure 2, the detention slaker itself consists of a mixing tank and integrated grit removal system. The mixing tank uses double-wall construction and is insulated to conserve heat and includes a hardened steel mixer impellor (Figure 5).

Figure 5: Chemco Detention Slaker Mixing Tank

Lime and dilution water are continuously fed into the mixing tank and are adjusted to maintain slaking temperature within +/- 1oF between the desired setpoint of 155 to 185oF. A pre-heater is provided to preheat the incoming water to 145oF during cold starts. Lime slurry is continuously produced and overflows into the grit separation tank (Figure 6) where a rotary screw removes grit particles. Because slurry is pumped from the large slurry storage tank, the slaker can be run at a lower rate for a period of time if temperature monitoring indicates that longer detention times are needed. Note that this is a manual adjustment that the operator would need to do. When the slaker is operating in “continuous mode”, the throughput of the slaker is adjusted based on slurry tank level to maintain a constant rate of production.

When the slurry tank is full, the slaker enters a standby mode. The slaker can also run in “batch mode”, where low slurry tank level initiates slaker start up and the slaker runs at approximately 90% capacity (where it operates most efficiently) until the slurry tank is full. The slaker then enters standby mode until the slurry tank empties. The batch mode may be useful during periods of low water demand. In standby mode the mixers, grit auger, and the dust and vapor management systems continue to run.

The relative inaccuracy of the rotary feeder (compared to a weight-based load cell) means that the slurry concentration varies somewhat during operation. Chemco’s control philosophy is to concentrate on maintaining a high slaker temperature with a tight control band to ensure proper slaking rather than focusing on maintaining a precise slurry mass concentration. Chemco believes that in practice, if the lime slurry is being controlled primarily by pH in the softener, the pH-control loop for the slurry feed pumps can easily increase or decrease pump speed to compensate, although there will be a slight delay.

Figure 6: Chemco Detention Slaker Degritter

De-gritted slurry would flow from each slaker into a dedicated 1,300-gallon slurry storage tank (two tanks total), which would be located in the basement. Slurry will be pumped from the tanks to the existing feed points using peristaltic hose pumps.

Operations and Maintenance activities for the Chemco detention slaker include:

• Periodic inspection of lime feeder and removal of accumulated lime pebbles or debris

• Cleaning of interior slaker walls and discharge weir. This a manual procedure involving hosing and scraping to remove accumulated scale which will form above the slurry surface level. Citric acid can be used if desired. Performed every 2 months.

• Check spray nozzles on weir and dust arrestor weekly for clogging

• Check for scaling on dust arrestor blower and eductor body

• Inspect grit auger for clogging

• Inspect and grease bearings

Figure 7 shows a Chemco detention slaker before and after a manual clean.

Figure 7: Chemco Detention Slaker Before and After a Manual Clean

The Chemco detention slaker system requires 10 cfm of plant air and 33 gpm of utility water.

3.2.2 Option 2: Chemco Batch Slaker

The scope of supply for the Chemco batch slaker system consists of the following major components:

• Two new silo discharge transitions and knife gates. SS Construction.

• Two 4000 lb/day 4-inch diameter volumetric screw feeders. 304 SS.

• Two batch slakers 1200 lb/hr at 10% slurry concentration (2400 lb/hr at 20%). 304 SS.

• Two 1300-gallon lime slurry storage tank. 304 SS.

• One Grit Removal Tank. 304 SS.

• Four lime slurry feed pumps (peristaltic hose pumps)

• Two lime system control panels

In the same manner as was proposed for the detention slaker, Chemco proposes to remove the existing day hoppers and install a new metal transition and a new actuated knife gate and directly feed lime from the existing silo to a volumetric feeder. The knife gate opens during the beginning of the batch process to allow lime into the slaker, then closes to keep steam out. For the batch slaker, a 4” diameter solid flight feed screw is used to meter dry lime into the slaker. The screw feeder is used rather than the rotary feeder used with the detention slaker to accommodate the larger size of the batch slaker tanks. The screw feeder is calibrated in the factory to deliver a certain volume of dry lime for each revolution of the feeder. This approach has moderate accuracy but is simple and inexpensive.

Chemco uses a dust and vapor management system to pull steam and dust out of the slaker headspace so that it does not cause fouling of the screw feeder. This vapor control system will result in much less fouling than is experienced with the current equipment. The slaking process operates up to 190oF, so it creates steam and humidity in the slaking chamber. The dust and vapor management system is designed to scrub the dust and prevent the hot, humid air from rising back into the feeder. If the air rises up into the feeder (of any type of slaker), the humidity in the air will pre-slake the CaO and cause clumping/clogging in the feeder. This leads to various feed issues. Each slaker will have a dust and vapor management system, which includes a stainless-steel canister with stainless steel spray nozzles and a draft inducing fan. This system is running when the slaker is ON and has an interlock to keep it running for a minimum of 6 hours after the slaker is turned OFF to prevent any residual humidity from rising into the feeder. The draft fan pulls the air across multiple spray nozzles that capture the dust. The water and dust are then recycled back into the grit process to not waste water. To avoid pulling a vacuum on the slaker, there is a clean air inlet strategically located on the discharge of the feeder. This way, the airflow is drawn through the feed chute, away from the feeder, to push the air away from the feeder.

As mentioned previously for the detention slaker, Chemco’s standard operating philosophy is to concentrate on maintaining a high slaker temperature with a tight control band (up to 190oF, +/- 1oF) to ensure proper slaking, without worrying about small inaccuracies in actual slurry composition due to inaccuracies in the volumetric feeders. Water to the slaker is accurately measured using a magnetic flow meter. Their logic is that if the lime slurry is being controlled primarily by pH in the softener, a pH-control loop for the slurry feed pumps will increase or decrease pump speed to compensate, so precise knowledge of the slurry concentration on a weight basis is not necessary. Because of the long detention times in the softener, small variations in mass feed rate are not noticed. Furthermore, Chemco notes that load cells measure both CaO and grit in the unslaked lime, so if the amount of grit varies batch to batch, this also adds an element of error if the load cell measurement is used to indicate the mass of CaO.

Chemco does offer an option to provide load cells for their batch slakers, if desired by Lompoc WTF staff, which can provide greater accuracy than a volumetric feeder. Load cells are supplied in addition to the volumetric feeder so that if a load cell fails, operation can continue using the volumetric feeder for lime measurement.

Chemco is proposing a batch slaker with a capacity of 1,200 lb/hr at 10% slurry concentration and 2,400 lb/hr at 20% slurry concentration. System feed rates will be automatically adjusted based on the operator-selected slurry concentration setpoint. The slaker will make 3 batches per hour with a cycle time of 20 min per batch. Each batch tank has a volume of 540 gallons. Because slaking is not continuous, to produce the same volume of slaked lime slurry the batch slaker tanks are larger than the detention slaker. As mentioned previously, the slaking reaction in the batch slaker is controlled by monitoring slaking temperature and adjusting lime/water feed. The Chemco batch slaker can automatically extend the slaking duration to maintain slaking temperature.

The batch slaker operates only when needed and in 20-minute batch cycles. The low-level in the lime slurry feed tank is set to correspond to a full batch of slurry. That way, when the full batch of slurry is released, there is enough available volume in the feed tank to accept a full batch. Chemco calibrates the low level setpoint slightly early to account for the 20-minute batch production cycle. Once the tank reaches a high level setpoint, the batch slaker will go into standby. The batch slaker program is also set up so it can produce multiple batches back-to-back in continuous operation; this is done during maximum dose demand to keep the tank at operational levels. The batch slaker goes through a rinse at the final stage of each batch. Because the tanks are all 304 stainless steel, citric acid can be manually added to clean the tanks (a manual clean is recommended once per year), but an automated acid clean system is not available.

The slaked lime slurry from each slakers will flow into a dedicated degritting tank prior to being sent to the slurry feed tank. An advantage of this configuration is that grit removal takes place before any slurry goes to the feed tank, minimizing the possibility of grit carrying over to the slurry feed tank and then clogging the injection system and minimizing grit abrasion in the slurry tanks.

Chemco has proposed direct-feed peristaltic hose pumps for this project. A duty and standby hose pump will be provided for each slaker system. Duty/standby pumps are recommended so that if the duty pump trips, the standby can be quickly started without having to switch slakers. The hose pumps are highly reliable and require less energy and are less expensive than a recirculation loop dosing arrangement.

Although Chemco can provide a loop system if requested, because the injection location into the sludge return line is so close to the slurry feed tanks, they do not believe that there are benefits to a loop system here.

Operations and Maintenance activities for the Chemco batch slaker include:

• Periodic (monthly) inspection of lime feeder and removal of accumulated lime pebbles or debris

• While minimal preventative maintenance is necessary, cleaning of interior slaker walls and discharge weir must be performed periodically. This a manual procedure involving hosing and scraping to remove accumulated scale. Acid can be used if desired. Performed yearly

• Check spray nozzles on weir and dust arrestor weekly for clogging

• Check for scaling on dust arrestor blower and eductor body

• Inspect grit auger for clogging

• Inspect and grease bearings

The Chemco batch system requires 15 cfm of plant air and 70 gpm of utility water.

3.2.3 Option 3: RDP Batch Slaker

RDP Technologies offers a Tekkem batch slaker that is characterized by a high degree of automation and precise measuring of the slurry concentration using load cells. The scope of supply for the RDP system consists of the following major components:

• Two new Dust Collectors for the existing silos

• Two new silo discharge transitions and knife gates

• Two 5200 lb/hr volumetric feeders with load cell control. Carbon steel.

• Two batch slakers capable of slaking 1000 lb/hr at a 10% slurry concentration and 2000 lb/hr at a

20% slurry concentration. 304 SS.

• Two 1000-gallon lime slurry storage tanks. 304 SS.

• Two fine grit classifiers. Wetted components 304 SS.

• Two lime slurry feed pumps and slurry feed loop with no-clog injectors

• Two lime system control panels

RDP proposes to remove the existing day hoppers and install a new metal transition and a new knife gate and directly feed lime from the existing silo with a 6-inch diameter screw feeder. An important feature of the RDP system is that lime feed is controlled gravimetrically rather than volumetrically. The lime slaker relies on load cells (Figure 8) to accurately measure the amounts of water and lime entering the reactor.

This results in a high degree of accuracy and consistency in the slurry strength produced by the slaker.

Because the screw feeder is used to move lime into the slaker but not to control the amount, RDP uses a larger diameter feeder than other manufacturers, which results in less clogging. The load cells do require maintenance, and if they fail they need to be serviced right away as there is no alternative measure of lime feed. RDP uses a dust and vapor management system to pull steam and dust out of the slaker headspace so that it does not cause fouling of the lime feeder.

Figure 8: RDP Load Cells

Slaker operation is as follows. The specified mass of lime is added to the reactor using direct weight measurement. Water is added at the appropriate water:lime ratio and the slaking temperature is monitored. The slaking reaction is allowed to run until the operator-set slaking temperature (185-195oF) is reached. The RDP system can operate at up to 195oF, which is higher than other manufacturers and results in a high-quality slaked product. Temperature is automatically controlled to match the setpoint within +/- 5oF. Based on the time required to reach temperature and the final slaking temperature, the slaker is programmed to adjust the water:lime ratio for the next batch to optimize slaking.

After the slaking reaction is complete, the slaker automatically dilutes the slurry to an operator-set value ranging between 10 and 20%, using the load cells to accurately meter the dilution water. The slurry concentration will be +/- 0.5% of the concentration set point. Slurry is then discharged to the slurry storage tank.

RDP recommends the use of their slurry recirculation loop for lime dosing and degritting. One lime slurry pump is provided for each slaker/storage tank system. The lime slurry pumps draw from the slurry storage tanks and send slurry around in a recirculating slurry feed loop that operates at approximately 120 gpm.

The continuous flow through the slurry loop at high velocity prevents settling of lime in the delivery lines.

Slurry is taken off of the recirculation loop through RDPs Precision Dosing Assemblies (Figure 9). These dosing assemblies consist of a non-contacting flow meter and a pinch-valve to accurately control slurry dosing. The Dosing Assembly also includes an enlarged settling zone ahead of the actual injection point to allow any grit to settle out instead of clogging the injector. Two Dosing Assemblies are provided on the recirculation loop – one for each clarifier sludge return dosing point.

Figure 9: RDP Dosing Assembly

The recirculation line continues past the dosing points to an external grit removal device (Figure 10). The RDP degritter uses a circular weir to achieve lower weir loading rates than a conventional straight weir and better grit removal.

Because slaked slurry goes directly to the slurry storage tank without first passing through a degritter, grit will be passed into the slurry tank from the slaker and this grit could clog conventional lime injectors. For this reason, RDP recommends using their slurry loop grit removal system as well as their precision dosing assembly, even though the lime injection location is so close to the slurry tanks. This does require more equipment and a larger 10 hp pump compared to the Chemco direct feed option with 2 hp hose pumps.

Figure 10: RDP Degritter

The RDP system also includes a patented semi-automated tank acid wash system to control scale buildup in the slaker reaction tank, the slurry storage tank and the interconnecting valve and the grit classifier. The system works by using the load cells to monitor the weight of the empty reaction tank.

When the weight increases, indicating scale buildup in the tank, an alarm is sent to indicate that a clean cycle should be initiated. Maintenance cleaning is initiated manually, requiring the Operator to take the slaker offline, add the required chemicals and initiate the acid cleaning routine via the System Control Panel. The cleaning sequence then proceeds to spray the acid solution into the reaction tank with the mixer operating to dissolve the accumulated scale. This solution is then discharged to the slurry aging tank and can be circulated to the lime slurry loop and de-gritter to clean them. The reaction between the lime scale and the acid results in a spent solution that is near-neutral in pH. This spent solution is typically discharged to the softener clarifier, but can optionally be blended with lime sludge prior to dewatering or disposal. The small volume of spent solution is diluted in the clarifier with no adverse effects on the overall softening reaction. Figure 11 shows before-clean and after-clean photos taken in 2023 from an RDP slaker that was installed in Saskatoon, Canada in 2009.

Figure 11: RDP Batch Slaker Mixing Tank Before and After Automated Cleaning Cycle

Operations and Maintenance activities for the RDP batch slaker include:

• Periodic inspection of lime feeder and removal of accumulated lime pebbles or debris

• Operator initiated automated acid-cleaning procedure. Performed as needed

• Check spray nozzles on weir and dust arrestor weekly for clogging

• Check for scaling on dust arrestor blower and eductor body

• Inspect grit auger for clogging

• Inspect and grease bearings

The RDP system requires 10 cfm of plant air and 85 gpm of utility water.

3.2.4 Comparison of Slaker Technologies

All three of the evaluated slaker technologies would be suitable for installation at the Lompoc WTP. All three technologies include full redundancy with two slakers (duty/standby), two degritting systems, two slurry storage tanks, and two slurry feed systems. All of the systems evaluated will provide more reliable service and lower maintenance effort than the existing slakers. Table 2 compares the main features of each system.

Table 2: Comparison of Lime Slaker Systems

Vendor Chemco Chemco RDP Slaker Type Detention Batch Batch

Capacity Range 1500 lb/hr at 10% slurry 2250 lb/hr at 15% slurry

1200 lb/hr at 10% slurry 2400 lb/hr at 20% slurry

1000 lb/hr at 10% slurry 2000 lb/hr at 20% slurry

Lime Feeder Volumetric Rotary Feeder 4”-Dia Volumetric Screw Feeder

(Load Cell optional)

6”-Dia Screw Feeder with Gravimetric Load Cell control

Dust and vapor management

Vacuum Vacuum Vacuum

Slaking Temperature Range

155 to 185oF +/- 1oF up to 190oF +/- 1oF 185 to 195oF +/- 5oF

Degritting System Integral with Slaker Separate between Slaker and Slurry Tank

Separate on Slurry Recirculation Loop after

Slurry Tank Slurry Injection System Hose pumps

(Recirculation loop optional)

Hose pumps (Recirculation loop optional)

Recirculation Loop with proprietary injection nozzles

Automated O&M Features

NA Automated water rinse Automated acid rinse

Connected hp 14 17.5 50 System Budget Cost $1,080,000 $1,300,000 $1,520,000 System Advantages Simple

Familiar technology Lowest cost

Grit removal ahead of slurry tank allows for use of simple hose pumps

Automated rinse reduces O&M efforts for tank cleaning Simple volumetric lime feed Grit removal ahead of slurry tank allows for use of simple hose pumps

Produces accurate and consistent slurry concentration Automated acid clean system greatly reduces O&M efforts for tank cleaning

System Disadvantages Limited control capability Lower slaking efficiency

Less accurate slurry concentration compared to RDP

Load cells require more maintenance than volumetric feeders

Grit removal downstream of slurry tank requires higher energy, higher complexity slurry loop feed system

3.3 SLAKER EQUIPMENT PROCUREMENT

Based on the technical considerations presented above and discussions with Lompoc operations and management, it is recommended to sole-source the procurement of a Chemco detention slaker for the final design. The Chemco detention slaker meets all project technical objectives, has received good references from prior users, is familiar technology to Lompoc staff, and represents a significant capital cost savings compared to the other slaker options reviewed.

In a project such as this where the majority of the engineering effort is accommodating a specific piece of equipment, the overall project proceeds much more quickly and efficiently if the equipment is pre-selected or pre-purchased prior to final design. This allows the design of the structural support elements, interconnecting piping, and electrical and controls to be done once to suit the specific requirements of the equipment.

The equipment procurement can be done in two general ways. Approach one involves having a general contractor include the specified equipment in their bid. Engineering design and general contract bid documents will be based on the dimensions of the Chemco equipment. The Chemco detention slaker would be specified as the only approved slaker equipment in the general contract and then procured by the general contractor. This simplifies the purchasing contract as the general contractor is the single contracting entity. However, this approach adds time to the overall project schedule in that Chemco cannot begin preparing shop drawings until after award of the general contract. Chemco estimates that a shop drawing submittal package would be submitted 14-18 weeks after the receipt of a purchase order, with equipment delivery 38-46 weeks after approval of shop drawings.

If the City pre-purchased the Chemco equipment separate from the installation contract, Chemco could begin the shop drawings at the same time as the engineering design is proceeding, based on the City’s purchase order. An installation contract package would be produced to cover the installation and commissioning of the slaker equipment. Fabrication and equipment delivery would likely be 6-months earlier with this approach. The drawback of this approach is that the pre-purchase and installation contract documents need to be carefully prepared to ensure that the scope of work for both the equipment supplier and installation contractor are carefully detailed in both contracts, including who is responsible for equipment shipping and unloading, installation, commissioning, coordination between trades, integration with plant controls, and overall system warranty. It would be in the City’s best interest to develop these purchasing documents such that the contractor would receive the equipment directly and hold responsibility for handling and storage, insurance, and protection prior to installation.

A preliminary technical specification for Lime Slaking equipment has been included in Appendix B.

4.0 BASIS OF DESIGN

The following system components will be replaced or updated as part of this project:

• Silo fill system piping reinforcement

• Silo ventilation and dust filter systems

• Storage silo knife gates

• Slakers

• Grit removal equipment and bins

• Slurry storage tanks and feed equipment

• Additional breaker in MCC-B

• Details of the proposed upgrades are described in the following sections.

4.1 PROCESS MECHANICAL

The overall process design basis was presented in Section 2.0. Details of the preferred Chemco detention slaker were presented in Section 3.2. Materials of construction for major pieces of equipment are shown in Table 3.

Table 3: Major Equipment Materials of Construction

Parameter Value Dry Lime Storage Silos Carbon Steel

Dry Lime Piping 304 Stainless Steel

Lime Feeders 304 Stainless Steel

Slakers 304 Stainless Steel

Aging Tanks 304 Stainless Steel

Fine Grit Classifiers and Screw Conveyors 304 Stainless Steel

Slurry Piping CPVC with Slurry Rated Hose at Transitions

CPVC = chlorinated polyvinyl chloride

To accommodate any of the systems evaluated, provision of 15 cfm of plant air at 100 psi and 85 gpm of utility water at 60 psi is required. The slurry feed pumps will need to pump against a backpressure of 45- 50 psi in the sludge return line.

4.2 STRUCTURAL

During the site visit in 2023, a set of as-built structural drawings (Sheet S-1 through S-12) was found, and this set contained sufficient information to perform the preliminary structural analysis. The existing Chemical Building was designed in 1961 and the design lateral loads would have been based on the 1958 Uniform Building Code. According to the General Note on Sheet S-1, this building was designed for Seismic Zone 3 which was the highest at the time of design.

The building is a 3-story steel structure supported by a one story, below-grade concrete basement, including concrete basement walls, concrete columns and beams, and a 4” thick concrete slab on the first floor. The lateral force resisting system of the existing steel structure above grade consists of Steel Ordinary Concentric Braced Frames (OCBFs), a 5” thick concrete floor diaphragm at the second and third levels, and a 1.5” 18GA steel deck roof diaphragm.

The RDP TEKKEM Slaking System Technical Proposal by RDP Technologies, Inc. (RDP), dated January 28, 2024, was used to provide the proposed equipment weights and locations, and is representative of both the RDP and Chemco equipment options. The current equipment weights are unknown (the mechanical as-built drawings and equipment cutsheets were not supplied). The general notes on Sheet S-1 of the as-built drawings indicated that 100 pounds per square foot (psf) live load was used for the design of the first floor and portions of second and third floor framing members. Per our preliminary analysis, the new equipment will increase the gravity load demand to the existing gravity load-carrying structural elements by greater than 5% but will increase the lateral load demand to the existing lateral load-carrying structural elements by less than 10%. According to Section 503 of 2022 California Existing Building Code (CEBC) with 2024 Supplement, no seismic retrofit is required for the existing lateral load-carrying elements. However, localized strengthening for gravity load-carrying structural elements is required.

The proposed equipment will be mainly on the first floor and basement floor, and some will be hung below the second floor. The existing first floor consists of a 4” thick concrete slab supported by 10” wide x 16” deep concrete beams spanning between the exterior walls and the concrete girders or columns. These beams are spaced at 7’-6” on center. Based on our preliminary analysis of the existing framing members with the provided equipment weights, it is recommended to place the new Lime Slakers on/near the existing concrete beam while the new Grit Classifiers shall be located between the concrete beams in a bay apart. For both Slakers and Classifiers, new steel beams shall be added beneath the existing slab at the anchor locations to transfer the loads to the concrete beams. The Lime Feeder shall be supported from the second-floor steel framing members for gravity and seismic loads. Refer to the preliminary sketches below.

There is a 4” thick concrete slab-on-grade (SOG) at the basement where the new Slurry Aging Tank, Slurry Loop Pump and an access platform are proposed to be located. Due to the clearance requirement indicated in RDP’s proposal, it is recommended to remove the existing 4” SOG and construct a new thicker foundation to support all new equipment. This new foundation shall be located in between the existing column footings on grids B and C. Refer to Figure 12, Figure 13, and Figure 14.

Figure 12: Preliminary Equipment Layout at First Floor

Figure 13: Preliminary Equipment Layout at Basement

Figure 14: Proposed Strengthening for New Equipment

During the Detailed Design phase, once the profiles and anchor patterns of equipment are available, more detailed strengthening of supports will be determined.

4.3 ELECTRICAL AND INSTRUMENTATION AND CONTROLS

The connected electrical loads for all three equipment options are summarized in Table 4. The RDP system has the highest connected power requirements, primarily due to the large slurry recirculation loop pumps, and was therefore used as the base proposal to evaluate electrical requirements for the project.

Table 4: Electrical Load List

Electrical Loads (hp) Chemco Detention Slaker

Chemco Batch Slaker

RDP Batch Slaker

Dust Collector fans (duty / standby) 2 x 3 hp

Lime Feeders (duty / standby) 2 x 0.5 hp 2 x 1.5 hp 2 x 3hp

Lime Slakers (duty / standby) 2 x 2.5 hp 2 x 3 hp 2 x 5 hp

Aging Tank Mixers (duty / standby) 2 x 2 hp 2 x 2 hp 2 x 3 hp

Grit Classifiers (duty / standby) Integrated with slaker

2 x 0.25 hp 2 x 1 hp

Lime Slurry Feed Pumps (duty / standby) 2 x 2 hp 2 x 2 hp 2 x 10 hp

Total Connected Power 14 hp 17.5 hp 50 hp

Power Supply 460-V, 3 phase, 60 Hz

460-V, 3 phase, 60 Hz

480-V, 3 phase, 60 Hz

The best option for powering the new lime slaker system is to use the spare bucket at MCC-B (Figure 15).

A new 175A circuit breaker would be added and used to provide power feed directly from MCC-B to new lime system. With this new circuit breaker, MCC B would be rated for 600A.

MCC B also provides power to three sump pumps, the two bin vibrators, and the flocculator motors. The slaker systems will operate in a duty/standby mode. The total running load was calculated as 150 A compared to the rated capacity of 600A.

Figure 15: Photo of the Existing MCC B Motor Control Center

Two control panels - a dedicated control panel for each lime slaker – will be provided and located on the main floor adjacent to the slakers. The lime slaker system control panels will include a human-machine graphical interface for use in controlling and accessing information regarding the system. The panel will include an Allen-Bradley CompactLogix programmable controller, which can be connected to a plant wide control and monitoring system. The panel will include a modem that would allow the lime slaker vendor to modify or adjust the operation of the system remotely for diagnostic and troubleshooting purposes.

Control panels will be NEMA 4X, with 304 SS enclosures.

The control panels will provide the following functions:

1. On/off control and starter for each motor

2. Slaker temperature setpoint and display of actual slaker temperature

3. Status of all valves, motors, and electrical components

4. Control of new silo dust collector equipment

5. Control of existing silo aeration and vibration equipment

Two smaller operator control panels will also be located in the basement adjacent to the slurry feed pumps to allow operators to monitor and adjust system settings from the lower level.

An HMI screen for the slakers will be added to the plant control system screens in the control room.

Preliminary Process Control Narrative

Lime will be dosed to into the sludge return pipe for each operating lime softener clarifier. A dedicated dosing injector with a flow control valve (for a recirculating loop feed) or a dedicated slurry pump (for direct feed) will be provided for each clarifier. Lime to each clarifier will be flow-paced based on ONLINE status of each clarifier and the corresponding clarifier inlet flow meter reading. The lime dose will be operator-entered in SCADA, then SCADA will calculate the lime slurry pump flow required to achieve the target dose at the clarifier inlet flowrate. SCADA will monitor the REMOTE status and POSITION of the flow control valve at the clarifier or the status of the direct dosing pump and alarm upon a FAIL or OUT OF POSITION status. SCADA will monitor and alarm upon a LOW FLOW condition.

Currently, the existing system has no automatic dosing adjustment based on online clarifier pH measurements. Clarifier pH is measured with grab samples and lime dose is manually adjusted by operations to achieve the desired pH setpoint. An online pH probe and feedback loop can be added for pH trim control of the lime slurry dosing, if desired.

4.4 CONSTRUCTION COORDINATION AND CONSTRAINTS

The construction approach for slaker replacement must account for maintaining continuous operation of the WTP process. The following constraints will be included in the project specifications to ensure that the selected Contractor maintains the overall schedule while continuously coordinating with plant operations:

• The equipment purchase specifications and the installation specifications must explicitly state that all equipment must be able to enter the building through the freight elevator, which has a capacity of 8000 lb.

• The Contractor must complete installation of the first new lime slaker, including start-up, testing, commissioning, and operator training, before demolishing the second lime slaker.

• Once beneficial use of the first new slaker is achieved, the City will go back to using the remaining existing slaker until the lime bin is emptied, prior to construction of the second…