providing customer support for sulfuric acid plants during the pandemic

Feature Providing customer support for sulfuric acid

plants during the pandemic By: Martha Villasenor, Regional Sales Manager, Weir Minerals

The Covid-19 pandemic has changed what customer support looks like for nearly all businesses and organizations worldwide. Sales and customer service teams are discovering new ways to provide help as social distancing and working remotely become the standard. What has not changed, however, is the need for customers to feel connected and know that they are supported. These fundamental aspects of caring for the customer remain essential in 2021.

Prior to the pandemic, we had the opportunity to visit acid plants around the globe. We went onsite and talked to the process, maintenance, purchasing, and engineering teams to learn about their needs, upcoming turnarounds, and new projects or expansions. These visits also allowed us to become acquainted with new hires, understand customer challenges, and offer advice on how to improve operational uptime based on examining wear patterns and specific scenarios.

As we entered the pandemic, all plants started to adapt to social distancing and enhanced safety protocols. Operation managers started coordinating teleconferences for internal meetings and it became very difficult to be on site physically. All matters were limited to phone conversations and online meetings. Roundtable events were also cancelled, which decreased the amount of information shared, resulting in a lack of understanding of new challenges in the customer’s operation. All of these changes are good and are essential to slowing the spread of Covid-19, but how do we still provide support without being onsite to discuss operational concerns face-to-face?

In addition, sulfuric acid plants suddenly faced a decrease in production due to a limited number of onsite staff and a decrease in demand as the global economy slowed. As the world realized that the Covid-19 pandemic was not going away soon, we had to reevaluate what it looked like to provide service and care to our customers. We understood that we had to adapt to the new landscape of people working remotely and figure out how to remain consistent, and even excel in providing support to our customers in this new normal.

One of the first items on our agenda was to reconnect with our customers. We held video conferences with our users and representatives providing training and seminars. We exchanged video recordings with our customers regarding onsite pump operations to learn about any new issues and monitor the existing equipment to ensure it was running properly. To accommodate the customer’s social distancing guidelines, we repeated several online sessions due to the limited number of people physically allowed in the conference room at the customer’s location. As supply chains required longer lead times, we were able to keep customers updated about delays quickly so they could react and plan ahead. While many companies were using these communication tools prior to Covid-19, they had not been exploited to the extent that was used during the peak of the pandemic.

As the pandemic continued and some restrictions were being lifted, it became possible to visit customers onsite for specific problems and needs by obtaining special approval and Covid-19 antigen tests. Some countries, like Chile, required us to be quarantined prior to our site visit. Cristian Gonzalez, a Weir Minerals product manager in Chile, talked about how he and his team had to follow strict guidelines provided by the Chilean government before visiting a customer’s operation to inspect one of their pumps when its performance decreased.

“In order to make the visit possible, we followed legal procedures to quarantine prior to the visit on site; applying for the permit and submitting all the requirements,” Cristian says. “The maintenance and process staff at this customer site were very grateful that we agreed to visit them and went through the government process to comply with Covid prevention regulations. In this particular case, the Superintendent went through all the steps to make sure we could get permission to be on site. We inspected the pumps that they were able to get out of the towers and bring to the workshop.”

During this visit, Cristian and his team found other pumps in the towers that the staff at the customer’s site could not bring to the workshop for inspection. The team suited up with appropriate PPE, went inside the tower, and realized that the suction strainer was blocked with ceramic fragments, resulting in starvation for one of the pumps. The team advised how this problem could be solved without buying unnecessary parts by focusing on the root cause. The customer was very thankful that Weir Minerals was willing to accommodate their request and provide a solution.

The maintenance superintendent at the site said, “Oftentimes, salespeople from other suppliers come and try to sell us their product even if there is no true need and we are misguided. We have to allocate our budget carefully and your honesty proves to us that your company has ethical professionals genuinely interested in helping us be cost effective and solve our problems.”

As employees started visiting customer sites under special requirements, it was refreshing that we could get to the customers who we struggled to reach via video conference. A smelter in Mexico has a policy that restricted the use of computers and cell phones except for a few key personnel. When we met with the Maintenance Manager at the site, we discussed 13 maintenance and process challenges and a solution for each one. We discovered why one of the pumps was drawing more amperage that eventually caused a process disruption when the motor breakers turned off. We were able to identify the pump and while it was almost identical to one of the pumps on another line (only ¼” difference on the impeller trim), we advised the customer not to use those pumps as the slightly smaller impeller would overload the pump’s motor. The pumps were not identical as the operator had assumed.

On another visit, we went to a sulfur chemicals plant in Mexico and met the newly hired Maintenance Superintendent. After the site visit, our Weir Minerals product manager in Mexico coordinated an online training in Spanish to familiarize the customer with the sulfuric acid nuances when using vertical pumps. The Maintenance Superintendent was very pleased to learn the capabilities Weir Minerals could provide for Lewis® pumps per the factory protocol.

“This plant used to have people that had decades of experience with Lewis pumps and they have all retired,” the Maintenance Superintendent said. “We find ourselves in a situation where the knowledge was not passed on and this reaching out from the Lewis representative and factory is of extreme relevance to our team and very much appreciated.”

The General Director expressed his satisfaction with the reliability of the pumps; the role they play in maximizing uptime for their operation; and why this knowledge is of extreme importance for the recently hired maintenance staff.

Cristian gonzalez, Weir Minerals product manager, suited up to inspect pump in absorption tower. Shield was removed from roller bearing in a failed maintenance attempt from third-party shop.

A recent inquiry was sent to one of the Weir Minerals sales engineers in Mexico for a plant that had been experiencing short life for the roller bearing. The Weir Minerals team had a video conference with the customer and discovered that the repair shop removed the shields from the roller bearing in an attempt to grease the bearings. This is not standard practice and is the main reason for the shortened life of the bearings. Weir Minerals also found that the customer obtained the bearing lock nut and washer from a third-party and did not use OEM spares. We were able to provide the solution and offer repairs and other services through one of our local service centers.

As the world evolves and acid plant knowledge diminishes with staff retiring, we need to use technology even more to exchange information, communicate, and solve problems for our customers. The Covid-19 pandemic has pushed us all to become more creative in working around physical limitations. The world will keep getting smaller as we bridge the physical and knowledge gaps with technology. Our business, like many others, has embraced this form of conducting business so we can be available anytime, anywhere.

Founded in 1871, The Weir Group PLC is a premium mining technology business whose purpose is to make customers’ operations more sustainable and efficient. The Group is ideally positioned to benefit from structural trends that support longterm demand for its technology including the need for more essential metals to support economic development and carbon transition. Weir’s highly engineered technology enables these critical resources to be produced with less energy, water, and waste - reducing customers’ total cost of ownership. The Group has 13,000 employees in over 60 countries.

For more information, visit www.global.weir. q

Department lESSONS lEarNEd: Case histories from the sulfuric acid industry

Hydrogen-generation and ignition in sulfuric

acid plants By: Chris Salgado & Walter Weiss, DuPont Clean Technologies

Hydrogen generation and ignition in sulfuric acid plants is an old and well discussed topic, but as we turn over industry personnel, it is advisable to keep it in front of experienced plant operators as well as fresh faces for whom it may be new material. This article offers a good general overview.

hydrogen formation

Hydrogen forms by way of the following overall chemical reaction:

Fe + H2SO4

 FeSO4 + H2

This reaction involves the exchange of electrons which the iron loses and the hydrogen gains. This type of reaction is called an electrochemical reaction and can be described in part by its two half-cell reactions involving the electron transfer as follows:

Fe  Fe++ + 2e− 2H+ + 2e−  H2

These equations balance both in terms of mass and electric charge. Neither mass nor energy is being created nor destroyed.

The iron oxidation reaction (loss of electrons) occurs at the metal surface, the anode, i.e. where the acid comes into contact with iron, nickel, or chromium equipment. The hydrogen reduction reaction occurs at the cathode, which, in the case of a sulfuric acid plant, is in the bulk solution. It can be shown in simple form using the classical electrochemical cell sketch in Fig. 1. The conductivity of the solution allows the transfer of electrons to occur more willingly. The higher the acid conductivity (i.e. the weaker the acid strength) the more rapidly this reaction can proceed.

Sulfuric acid plants are comprised primarily of various steels in the strong acid system, so iron is a necessity. Acid

condensation or maintenance of the right acid concentration in the sulfuric acid plant environment is governed by the plant design and controlled during operation to minimize the risk of iron (or nickel or chromium) corrosion and resulting hydrogen evolution. Yet there are certain baseline levels of corrosion and hence baseline levels of hydrogen evolution that occur on a continuous basis. With good concentration control, this level of hydrogen generation vis-a-vis the gas flowrate is almost undetectable. Most plant operators are not aware that it is present.

anode (positive)

oxidation electron loss

X- X+e

anions (negative) cations (positive)

electrolyte cathode (negative)

reduction electron gain

M++ e M

Fig. 1: Simplified sketch of electron exchange involved in hydrogen formation in a sulfuric acid plant.

the impact of process technology changes

The relative surface area of steel within an acid plant has increased over time with advances in the process technology. Introduction of new flow schemes and new equipment designs has provided high points where the hydrogen may collect if not continuously removed. These changes over the last fifty years have generated a relatively new set of risk concerns and requirements for operator attention.

As noted, corrosion in sulfuric acid plants generates hydrogen. Contact of metal surfaces with weak acid can increase corrosion rates of these metals by several orders of magnitude. As corrosion rates rise, hydrogen generation rates also increase. Over time, hydrogen forms gas bubbles in the acid. The movement of gas bubbles flowing through the acid can disturb the passive oxide or sulfate film that builds up on surfaces containing sulfuric acid, in turn further increasing corrosion rates.

Limiting corrosion

Many common materials used in acid plants cause only acceptable corrosion rates within relatively small concentration ranges and temperature ranges. Acid velocity may also have an effect. Equipment and piping must be kept within their prescribed operating windows to keep corrosion rates low. It is critical to monitor and maintain appropriate instrumentation for leak detection around equipment such as acid coolers that have water and acid on opposing sides of metal tubes. Response to acid cooler leaks must be swift to minimize equipment damage and hydrogen generation. Not only will the water rapidly dilute acid outside of the desired concentration range for the acid cooler materials, but additional heat will also be generated. Acid dilution produces heat, and corrosion rates increase with rises in acid temperature. Corrosion rates therefore intensify dramatically during an acid cooler leak.

The same can be said for loss of acid system concentration control–via control loop failure or from an upstream steam system leak. As in the cooler leak example described earlier, the correct response includes quick detection and (1) rapid separation of the water source from the acid as well as (2) a quick de-inventory of the acid plant equipment. Once the weaker acid is removed from the system, and the system is re-inventoried with circulating strong acid, the corrosion rate subsides, and the amount of hydrogen generation returns to more normal levels.

Preventing hydrogen ignition

The elements needed for a fire are fuel, an oxidant, and an ignition source. The elements needed for an explosion are the same as those needed for a fire, but the fuel and oxidant must be mixed and located in a confined space. For hydrogen to ignite at its lower explosive limit (LEL), the energy required is very low–almost undetectable.

Hydrogen is a very effective fuel and is extremely buoyant and diffusive. Hydrogen will normally flow through an acid plant with the bulk gas and be carried out of the stack in low concentration levels. But in a stagnant plant, or a plant with low air movement, hydrogen can accumulate in high points, such as in the tops of acid towers. Because hydrogen is diffusive, it mixes well with process gas which contains oxygen. Even normal process gases such as NO2, NO, and SO2 can participate in the reaction–reducing the LEL and increasing the energy release. Once hydrogen builds up to a value exceeding its lower explosive limit of 4% (or less), an ignition source will start a fire. If these elements are located within a confined space, an ignition source will cause an explosion. There are many confined spaces within an acid plant.

The key point is worth repeating: operation of the acid plant’s main compressor will help to reduce hydrogen concentrations and minimize the confined space risk factor. However, if the main compressor is shut down by either intent or by interlock, the risk of fire and explosion can increase dramatically. It should be stressed once again that maintaining the air flow to purge the plant is key–bypassing and overriding interlocks if necessary.

It is also worth noting that in the last decade or so, there have been an average of one or two hydrogen explosion incidents per year, mostly or almost entirely once the plant has been shut down. The energy release even at LEL concentrations is adequate to significantly damage equipment, cause extensive down time, and incur hefty repair costs. And, most importantly, these incidents can put personnel in harm’s way.

Purging the plant prior to entering a shutdown will help flush hydrogen out of the plant. Installing high point vents in accessible locations and opening those vents after purging the plant will help release hydrogen that can continue to form. Use of automated valves is recommended to speed response time and to separate workers opening the valves from the explosion potential. Isolating equipment, draining acid and water from equipment, and rapidly reacting to concentration or temperature upsets can help minimize hydrogen generation. In addition, ensuring there are effective concentration controls, dilution water interlocks, and process alarms will help reduce risk of a hydrogen incident.

Conclusion

Facilities need to take steps to prevent hydrogen incidents: develop and drill emergency procedures, conduct operator training focusing on hydrogen awareness, and consider hydrogen for general work or hot work permitting to minimize hydrogen risks.

Other steps plants can take include preventing equipment failures by implementing a mechanical integrity program, conducting routine turnaround inspections and equipment repairs, replacing equipment prior to failures, and carefully monitoring process conditions. In other words, the aim is to prevent leaks from occurring in the first place.

Safely starting up, operating, shutting down, and maintaining sulfuric acid plants are thus the keys to minimizing the risk of an incident caused by the presence of hydrogen.

For more information, visit cleantechnologies.dupont. com or email Chris Salgado at Christopher.Salgado@ dupont.com. q